That's a really tricky thing. So far the Everdrives lack basically all of the extra features except for RTC. The Game Boy had so many additions. Rumble, motion etc. Where are these features? Yeah, of course you can patch the ROMs to not use them. But that's not the real experience then.
I believe that the Everdrive GBA Pro was made only to be able to compete with the EZ-Flash OMEGA Definitive Edition which is superior to the current Everdrive GBA in basically all ways. If adding sensors for a few games was something krikzz was interested in, it would've been done many years ago. But because of the strong competition, there has to be a new Everdrive GBA because EZ-Flash can't be beat in price and only in features.
Also, the EZ-Flash OMEGA DE is to date the only GBA flashcart to support GBA movie ROMs that are 64MB. Not even the new Everdrive GBA Pro will support them, as it doesn't have enough memory to keep it.
Speaking of memory, where is FRAM for savegames? Why does the PRO everdrive use battery backed SRAM? (to be fair: this is not confirmed yet but the specs of the card only mention a SRAM storage so it will save to SRAM).