Those four geographical possibilities lead to some possibly unique situations:

There's never been an all-L.A. world series.

There's never been a Baltimore-Washington world series.

There's been only one St. Louis-Kansas City world series, in 1985 (Also the Royals' last postseason appearance)

There's been only one all-Bay Area world series (1989)

Although my favorite teams are out of it, I'm looking forward to some new cities this year! Variety's great.