Deoxys Neutral is just Mega Alakazam with a crappy ability and can go mixed. Oh, it can throw hazards around, but doesn't have the bulk to do it repeatedly. It's probably safe to come down. It would be S-Rank for sure, but yeah, it'd be fine.
Reshiram 2 Hit KO's almost everything in the tier. It's staying in ubers.
Genesect would probably be fine. It proably won't come down, though, because it has tons of different sets, and smogon likes it when things only have 1 or 2 so you can counter them easier, something like "restricting teambuilding" or some such nonsense.
I was always against banning Greninja. It sucks in Ubers, bring it back. I liked Greninja OU.
Mega Mawile was also fine. Sure, it's really, really good, but it's on the same level as Mega Metagross, which is fine. It doesn't need to be in ubers either.