I didn't even know Retro-Bit was making a new system until you said something, and I'd like to submit that after researching it a bit, I think I'd actually go with the Super Retro Trio over the Retron 5 at this point; if I want to play an emulator, I've got all the resources to play one without buying the Retron 5. I don't really understand Hyperkin's need to give retro systems stuff like a front-end GUI, unless they're trying to present "retro" gaming to the younger generation of gamers by offering a system interface similar to the consoles of today to ease the transition. I dunno.
Hyperkin is casting a broader net than RetroBit is. Retrobit is going with another reverse engineered hardware clone, making it pretty much like every other clone they, Hyperkin, and Yobo have released up to this point. On the surface, it seems strange since it will retail for likely around the same price as the Retron5 but do far less. On the other hand, as mentioned, Retrobit and Hyperkin are going after completely different philosophies with their respective devices. There are a lot of retro gamers who feel the way you do - if it ain't on a CRT, it's ain't worth playing.
I welcome both, and will be buying both for comparison sake. The Retron5 has some clear advantages - some obvious, some not. In addition to native 720p/1080p HDMI support, the Retron5 has real potential for 100% software support; even if the emulators it runs aren't 100% right at launch, the thing can be firmware updated. This is a big contrast to the Retro Trio. Outside of possibly some minor tweaking, the games that do or don't work with it at launch will be like that forever.
Wouldn't the GBA format, by design, also support GB and GBC?
RetroBit and Hyperkin have been announced their systems will both play GB and GBC games as well, but the direct answer to your question is no, the GBA format does not by design also support GB and GBC. The GBA had it's own brand new processor and an additional one for GBC that was also backwards compatible with original GB. The GameBoy Micro released in 2005 does not have the GBC Z-80 processor, which is why it can't play GBC or GB games. The same is true with the DS and DS Lite. GBA games will work, but not GBC/GB because it lacks the hardware. In more recent years, GBA SP clones out of China also lack the Z-80. GBA does not mean GB/GBC.
I'm also unfamiliar with the Famicom cartridge format; other than their physical size difference, are there any big differences between FC carts and NES carts that would stop them from plugging into the same slot? I ask because the SRT has a region-switch toggle built-in (labeled are options for: NTSC, PF, NJ, PA), which I imagine would support FC carts if the format isn't too dissimilar from NES, and then it would match the compatibility of the Retron 5 perfectly.
You're opening a big can o' worms here, but I'll try to keep things simple. The Famicom and NES are the same hardware, but there are some important differences. Chief among them, the cartridge connectors are physically shaped differently and the Famicom has address lines that are unused on NES systems. In Japan, the Famicom had devices such as a BASIC programmig keyboard, a data recorder, even a karaoke machine attachment. Also some games also had built in additional soundchips enabling richer audio than the system itself could provide.
Hyperkin is including the Famicom port as a nice gesture since Famicom gaming is a small but active part of the retro gaming community. It means no adapter is required, and also they will be able to market the Retron5 as-is on a global basis in the Asia-Pacific region as a all in one clone that will play Famicom, Super Famicom, MegaDrive and more - even the mysterious "NES" format.

Region switching though is where things get a little complicated. I'm pretty sure the Region Switch of the Retro Trio will only be for MegaDrive games. NES and Famicom are region free, but problems arise when you take Europe into account. For whatever reason, Nintendo chose to release the NES there with a slower clockspeed - 1.66Mhz compared to 1.79Mhz. Since the NES cpu rendered graphics, input and audio all internally, this 17% difference means that PAL NES games are 17%
slower in response, speed and audio. If you try to play these on an NTSC system, those games will be 17%
faster than they should - creating new problems. RetroBit would need to put in two NOACs to address this, and I don't see them doing that.
Also SNES is in the same boat, but for different reasons. Nintendo did place a NTSC/PAL region lock in software around 1993, but since that's software and not hardware, they own the patent to that and could legally sue clone makers who bypass it. Since GB/GBC/GBA are region free too, more than likely, that region switch on the Retro Trio is for MegaDrive/Genesis games only.
Also, the Retron 5 will have its legacy controller ports on the sides of the system. The SRT will have ports for NES, SNES and Genesis controllers (2 each) on the front of the system. For me, this would make it easier to consolidate space in my gaming area.
I do see what you're saying, but keep in mind those controllers are all optional on the Retron5 - it'll come with a funky bluetooth controller that appears to have a Neo-GeoZ style cllckstick. Granted, no judgements can be passed on it until it's actually released, but it at least has potential to be pretty damn sweet. And Hyperkin has also said that you'll be able to use any of the controllers to play any system, so just a single SNES controller will work with Genesis, NES or GBA. It's not necessarily going to be the octopus the Retorn3 was unless you want it to be.
For me, the biggest disadvantage of either system is the fact that neither the Sega CD nor the 32X are likely to be compatible at all.
Really?? Hyperkin isn't doing that because the market potential just isn't there. Very few retro gamers give a crap at all about the MegaDrive's life support add ons. I had both growing up, but there's nothing on 32X I could not live without, and Although it would be amusing for there to be a 1x CD drive on the bottom of the Retron5, it would drive up costs and I don't think it's worth it.
Although its too niche to happen, I'd like PC Engine and TurboGraphix16 support in modern clones. NEC's pseudo 16 bit console has some great classic games, and it wouldn't be too difficult to reverse engineer the original PC Engine hardware. Only reason it's not done is because it doesn't have global appeal in the same way the NES, SNES and Genesis do.
I'd also need to know for personal reasons if the SRT can output NES games via S-Video.
Not even chance. Unless RetroBit completely redesigns the NOAC from the ground up, (that means serious R&D) this will never, ever happen. The Famicom/NES has a PPU that is incapable of S-Video, becuase S-Video comes from RGB which the NES is also incapable of. Only Nintendo Arcade Machines based on the Famicom hardware had RGB ready PPUs for arcade raster monitors, as well as an extremely rare and expensive variant of the Famicom.
All NOACs (Nintendo On A Chip)s are based on the original Famicom hardware. No S-Video there, no S-Video in the NOAC. It's pretty simple. RetroBit systems of the past have actually trickily incorporated S-Video into the NES compatible clones, but they always do so by feeding the NES' native Composite video through the S-Video Luma line, which by itself is unshielded without its grounds making it actually worse than just using the yellow composite jack.
I'd flip my sh*t if RetroBit did S-Video via RGB for NES in their upcoming clone, but it won't happen unless they either completely redesign the NOAC from the ground up or add an FPGA to do that, which would double the price ($200 at least).
In this battle, Hyperkin has the clear clear advantage going with emulation. Hell they could even include an option to use the RGB color pallet on a whim.