Across The Sea of Years

A dual stated adventure across Time and Space for.... well that is what I don't know yet.

I have always toyed with the idea of running a game at a con, say like Gen Con where I have multiple days, where it is the same group of characters, or their reincarnations or their children, across time and different systems.   My systems of choice would be Unisystem and some flavor of D&D.  Likely Basic.

I have done similar ideas in Season of the Witch, where I took in ideas from different games to get a different feel.  Generation HEX was conceived as using a different system each game, but that never worked out.

This idea though is two plan a game that takes place in the past, present and maybe future.  Each game is seperate unto itself, but builds a bigger story.

One idea I had was a adventure named "Synchronicity" where characters from Ghosts of Albion meet up with their counterparts from Buffy.  But that is only one, albeit long, game. Plus the system for Ghosts and Buffy is the same.

Another game I have played before is Blight for Ghosts of Albion.  It takes place in 1847 and is an unofficial sequel to my Dark Druid for Buffy (that takes place in an alternate 2001). There is a third adventure in the mix, All Souls Night, which was always designed to go with my Eire game.
I would retool Blight just a bit.  But the Dark Druid is designed for new characters, so the big bad introduced is not all that big and bad.  It works though if I run them in something like a past life regression.

The other idea I had was an adventure around the rise and fall of Elizabeth Bathory.
D&D for when she was alive and you have to stop her (though to be 100% fair, an adventure like that screams LotFP), Ghosts of Albion when she is prowling the streets of Victorian London, and something else (Call of Cthulhu maybe) for later.

I have also over the years toyed with the idea of Doctor Who, Star Frontiers, and Alternity (yeah I have been thinking about this one for a while) for the future.  I think the idea came to me when I wanted to run a hunt Jack the Ripper and I thought back to the old Star Trek episode "A Wolf in the Fold" and to the movie "Time After Time".  Jack the Ripper is still an interesting idea. A time traveling serial killer/entity could make a fun opponent.

Lots of ideas really, but nothing has really jelled yet for me.  Once I have the right story idea and roll for the characters then the system will be easier to decide on.

Anyone done anything like this before?  What did you do and what did you use?