I'm still confused, at what, if anything, the AVS supports that the standard NES/Famicom doesn't, besides extra sprites and Four Score Pro support (and the four score is a modded accessory that will work with any NES). Homebrews have already come out that improved/smoother display using extra sprites, Scramble being a good example, but bitd games were improved as well. It also seems some games suffer slightly less slowdown with extra sprites enabled, but what other magical features (beside scoreboard) does the AVS do that an NES or FC can't? Don't forget also the Analogue NT Mini uses a different FPGA solution to AVS (though it also supports extra sprite mode) and is a somewhat popular competing option. If any extra features were added to AVS hardware, it may break existing games or become buggy, and unless NT and AVS cooperated, the userbase would be fragmented even among owners of HDMI systems (HiDef NES, NT Mini, or AVS).
I simply don't see what functionality exists within the firmware that can be taken advantage of besides extra sprites. And relying on this mode being toggled on for proper operation would make the game a glitch fest on an original NES, or even an AVS / NT Mini with the extra sprites turned off.
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~From the Nintendo/Atari addict formerly known as StarDust4Ever...