TsarbucksMaybe you can make it a new and retro pug group. You can have what you said, as well as GPit, Coalplant, Logjam, etc.
I've tried this idea before, and it's unappealing to most players as they're playing maps that have usually been long gone from the 6s map rotation and are usually gone for good reason. The majority of players don't seem to want to play older maps due to both the unappealing thought of playing an old map with the massive playstyle change that's happened in the years since that map's release or because it just doesn't benefit anyone if it's never going to be in rotation again.
I mention adding a map like Gravelpit because while its playstyle is very different to today's TF2, I feel like it definitely provides some much needed diversity in the TF2 map pool, and would be a nice example of a map that showcases team coordination, rotation, and a more fluid class choice over today's cp_whatever. That's not to say the majority of cp maps are poorly designed (quite the contrary, props to mapmakers like chojje and Phi), just that it would be very nice to see other gamemodes integrated into 6vs6.
The point of this group is really more of trying out some different maps (mostly new) to see if they'd be fun to run in the current map pool provided we use ESEA configs and whitelists.