Theme Name: Civilizations
Characters: One or two time travelers and, dependent on the civilization of the release, thinking Aztecs, Egyptians, Cavepeople, Babylonians, Vikings, etc...
Conflict: If there needs to be one rather than exploratory, maybe a race (against evil guys) to collect items from different civilizations to bring back to the future to unlock "a great truth"
Setting: All over...and dependent on release...maybe Ancient Egypt sets for one release, Ancient Rome for another...
Background Info: This would need to be tied into some ongoing comic or something for backstory but the general premise is that 2 individuals have come upon the means to travel through time. Initially I'm envisioning a exploratory adventure (i.e. visit new civilizations and dress the part) but a sub-theme could be added where they must collect items from the past to unlock "something".
Ancient Egypt could include sets ranging from small chariots and bazaar stands to temples or small pyramids...the artifact here could be a golden cat or something, which could be randomly distributed among the sets...(ratio 4 out of 5) to add a hunt component. The next release could be sets surrounding Ancient Rome with small shops and temples...
Yes, needs some more work but I think you can get the idea!
PS. and not like that Time-twisters theme back in the 90s...the concentration here would be on the Civilizations visited and not vehicles.
PPS. And when those are covered they can move forward and visit other Cultures....Oriental, Wild West,...