I can only repeat my previous suggestions:
1. Vintage TF: no hats except on buildings, no unlockables, pre-unlock mechanics (pyro can't deflect, sniper has 0.2s lag on scoping, spy can only stab in the back, not just anywhere except chest and face), vanilla map rotation.
Pro: old farts like me think it's cool. It's also unheard of, so panda.tf might be the first community to have such a server (I mean, permanently. I know there were attempts at that before).
Con: like with anything new, it might require a bit of work to get people to like it.
2. Scoutmod (as shown
here): infinite double jumps, 1sec ball recharge.
Pro: it's hella fun! Also, from what I know about sourcemod, it's relatively easy to do.
Con: my knowledge isn't enough to make this mod, nor do I know where to get it. Ron's gone, too.
3. 100% crit server with only custom wacky maps on rotation
Pro: it's hella fun! Also, with 100% crit, there's no need to refrain from adding rtd there.
Con: kinda hard to balance the number of players. From my experience, I advise 14.
4. Additional dm_duel server with random ranged crits disabled
Pro: will require more skillz! ^_^
Con: will require more skillz! T_T