Yeah, for once I largely agree with pbj. Once you start heavily hacking these devices, you undermine the plug and play simplicity which is their main usp. When I eventually get round to hacking my SNES Mini, I intend to just add a handful of extra games, and maybe the option to activate reset from the controller. And that will be it.
That being said, I can kind of see the appeal of adding more flash memory. The onboard memory is extremely tight. Unfortunately, if you add too many games, you rapidly lose the ability to use save states, as SNES save states are apparently very memory hungry.
So I think adding extra external flash memory probably makes sense as long as it gets incorporated into Hakchi, and thus becomes trivial to do.