Bourbon barrel Porter comes to mind...you can get the oak from the cask
and add bourbon to your liking.
Strong Dark Belgian for the red wine bbl
A flemmish thing like the Dutchess but beware it gets close to the vinegar zone.
Or any beer of choice that you can think would be enhanced with the old remnants
of the wood's previous occupant....You can always sour with new bugs, brett, pedio,Lacto etc.
Every decision you make will change the contents. Think of this as a work in progress
rather than a one time brew. Imagine putting an imperial stout together in a cask to set
it sailing upon the long voyage to the russian courtisans......