Just found out this thing exists and will be available soonish. How does the community feel about this and other FPGA solutions such as the Analogue NT for speedrunning? http://stephens-projects.com/projects/gbahdmi/

Admittedly I know very little about this, but if it's what I think it is and it just outputs what would be on the GBA screen to HDMI then I don't see why there would be a problem with it, since it would pretty much be the equivalent of a DS or 3DS capture card. That being said, not all GBA game communities may agree on this, so you'd have to bring it up with the community for whatever game(s) you're planning to run with it.

The FPGA part of this mod does not effect the system at all because all it is doing is taking the data pins from the screen, audio, and clock and upscaling the output to 720p for HDMI. Now what is changed when performing this mod is the oscillator which increases the clock speed of the GBA from 59.73 to 60hz. This is done because HDMI is picky and there is not a lot of leeway with refresh rate. This will cause the system to run slightly faster but this is the same thing which the Gamecube does with the Gameboy player (from 59.73 to 59.94 hz) but just poorly as is why there are stutter issues with it. So since the Gameboy player is usually accepted I would assume there to be no problem with this mod in the community and more than likely will be universally accepted.