Been trying to get into other games and mostly want to avoid the hassle of hooking up a million consoles. I've already purchased a Super Retro Advance, which lets me play GBA games on my SNES. Works really fine, albeit a terrrible 3:2 composite only video display.

Also noticed they made one for a genesis-on-snes adapter as well (which further lets you play SMS games on it).

Has anyone else looked into these kind of conversions and whether they'd be considered acceptable for speedruns? From my testing of the GBA-on-SNES, all the games seemed fine to me.

I don't know about Super Retro Advance being acceptable or not, but I'd love to know.

However, the Super Game Boy 2 is acceptable for playing game boy games on the SNES/Famicom. The Gameboy player for the Gamecube is acceptable for playing GB/GBC/GBA games on the Gamecube. Backwards compatibility is generally accepted everywhere. So PS2 works for PSX, the PSX/2 games that are on the PS4 are fine.

Generally speaking, anything that is a multiconsole though, like the Retron 5 or anything like that, are not alright. They're just emulators, and not very accurate ones at that.

I'm talking about the unofficial means that use real consoles (not aftermarket ones like retrons). For instances 3rd party gba player for snes, Genesis on Snes (which further allows for sega master drive on snes), NES on SNES, etc.

That's my point. Generally speaking, if it's not on that list, it would only be allowed for speed runs on a case by case basis because of inaccuracies, or because it's just emulation.