Do you think you could ever fix the scaling? PocketNES mode is almost fine, but the picture is shifted down, obscuring things. (I mean there's a black bar at the top of the screen, and it's cut off at the bottom.)
What game(s) are you trying to run ? Every single one of them is different in this regard. You can default to no crop in all cases : it will show everything onscreen and squeeze it down to 240x160. (of course, it won't look as good as PocketNES in an ideal setting)
Premature optimization is the root of all evil. You're doing all this for a <1% performance increase, when you could get a 10% boost by just rewritting some code. There are much better optimizations you could do without messing with the OS.
Yes, in an ideal world, i would have implemented a 6502 MIPS dynarec for fceux. But i'm no assembly programmer (sorry to disappoint you guys) and getting those 10% is not always feasible that easily without rewrite much of it. In comparison, getting that 1% (or less) was much easier and don't require much work on my part.
I mean even you are seeing that reGBA does not always run smoothly despite the fairly good MIPS dynarec it has (as you may have noticed in the comments). That's not to mention the broken games on it, which is just as important.
That's not how it works. If I want to add PulseAudio to the OS, and all the apps are statically linked, then as soon as the OS update lands you would lose audio for all the apps, until they are recompiled, and everybody would blame the firmware devs for breaking everything. So then we wouldn't be able to update anything to keep compatibility with static apps and avoid complaints. That's how a firmware dies.
Not sure how the Pulseaudio daemon works but yeah i guess it is a possibility that it could break if the static library happens not to be compatible with the newer version. Thankfully though, we are not using pulseaudio on that handled as it would be overkill.
I would consider using the dynamic libraries on a more powerful handled like the GCW0 but not on the RS-90.