Ok so let me just dive straight in...
1st) My first idea was a tf2007 server, which is where their is a server with the original pre-packaged map rotation and no access to the item server and the original stock weapon stats....
2nd)My second idea was a little more original but less easy to accomplish, so I propose a "original stat weapon server" now what is this your asking? it's a callback to original stats of weapons, so for example instead of the rocket and sticky jumper users not allowed to carry briefcases they are now allowed to thanks to the original stat, the ullapool caber would have it's classic pullout time, and the dead ringer would be to op....
Any who that's all I've got for now and hope I have given some good ideas have a safe and nice day!!!
Edit: A new idea came to thought where we could incorporate other game mechanics into team fortress 2 like for example mario, sonic, metroid, halo, counter strike, portal, etc. but this idea is not a main one as that junk is probably for gmod