All of the good stuff has already been mentioned by other members, so I'd just go with a simple one... Having the ability to use non-default themes again ^{[e.g. BlackBox theme]}. I do know it was "disabled to reduce the attack surface", but perhaps the changes that were made in the past 9 years could provide enough protection to restore that feature ^{[I'm well aware of the alternative routes, but I prefer not to use something that isn't "officially" part of the forum]}.