Functunal Reprint in Standard Deck
This may be more of a personal preference, but if it's against the rules, even if it technically doesn't matter this time, I'm highly unlikely to make an exception. Does it create a feel bad moment now? Yes, but I don't want something happening in the future and let people have “you let that guy do that, why can't I do this?” to fall back on.
I would allow him to play Indriks if he could get them reasonably quickly, but that's it, and only because regular is supposed to emphasize fun.