In the hypothetical revival of CoH, I would love to see the Praetorian content expanded- continue the Loyalist/Resistance arcs through First Ward and beyond (the Lore AMA for 2014 mentions theoretical plans for a 40+ Neo-Tokyo arc).
Kallisti Wharf brought through to completion, of course. And some expansions/revitalizations of several of the existing and underutilized Blue and Red Zones- King's Row got some changes in i24, but it would be cool to see that expanded upon (notably with some of the "Turf War" changes mentioned in the AMA); of course Boomtown. Bricks also got some i24 changes that were nice, but I'd still like to see Crey's Folly revamped (perhaps turn it into a resettlement zone for Restructurist Rikti?)
Of course, tying red and blue sides together more directly would also be great (although I don't want PvP to be mandatory; perhaps as some kind of "opt-in"?)