Just an idea to throw out there for discussion.
I've noticed this on a couple of other sites, but I think Armorama.com does it best. If you look under their
Campaigns section, you'll find some good stuff. They'll pick a general theme and actually have it fairly open.
Applying it back to the discussion at hand, a couple of ideas:
1) Allied Armour Theme - maybe pick a season/year and keep it open to any allied armor which would have been used in that timeframe?
2) Sherman Theme - limit it to any variant of the Sherman.
3) US Armor - Then & Now - okay very wide open, but would allow Shermans and M1s. Maybe call it the US Armor in Europe and let it be any US tank which saw service in Europe?
Some ideas, that's all.