Well, I guess it's a bit late to answer the OP, but here goes:
Hard to say - I guess these were the builds I look fondly back on. It's hard to say how this would work with all the changes since then but some of these I would *love* to see:
Minion limit - I still VERY fondly remember having huge armies. I find that the changes to Verata's Sacrifice and Blood of the Master (especially with AI and the possibility of multiple MM's in a few missions) would be interesting on top of that. I think that, PvE wise this would still mostly be "balanced" as the old method of long lived minions is no more - BOTM would quickly become a one skill insta-death of the MM

This is the only one I *really* want but I don't really expect it.
The paragon. The paragon definitely has it's "Imbagon" thing going and no question that is quite powerful - however I *really* liked playing some of the early holding builds that were out well before PvE only skills (see a thread by Lord Helmo for the build I am thinking of). Unfortunately I do not see this one happening as it would make the paragon too good in PvE with the PvE only skills out there. Even though it wasn't really a core part of the above mentioned build I would like to see the recharge for "Go for the Eyes" removed.
Spiritual Pain - LOTS of fun with that one. Because of the general lack of spirits this wasn't used too much. However it was powerful enough that it was worth wasting a skill slot in general for those cases - also nothing like the satisfaction of all the gold numbers floating in the air.
Splinter Weapon - lots of nice gold numbers. Again, not really overpowered in PvE and more than just the barrage'rs used it. IIRC the reasoning given for it had to do with VoD or some other PvP specific environmental effect.
*shrug* IMO skills that are generally unbalanced in PvP are also overpowered in PvE and both should share the buffs/nerfs. The ones I don't like are ones that require a specific team build to take advantage of, a specific PvP area effect (say Victory or Death), or a specific PvP circumstance (too easy/too hard with respect to killing the guild lords). Obviously those PvP instances aren't happening in PvE and it's too hard - in general - to get those really powerful PvP team builds outside of a few larger guilds.
I hate (but I do understand so I normally do not complain as there was no other choice) when my OK build with my hench/heroes is nerfed to oblivion because four of us, two monks, a MM and, and a SF ele wins at VoD in a GvG battle. Especially being that I and 99% of the GW population will never have said team setup nor will we ever have the VoD affect on us (again - read above - I fully understand and support PvP based balances).
I'll be happy if they separate them intelligently from here on out even if there are no skill reversions. Especially true if this continues into GW2. How ti works out will be interesting.