2028: William Paul(L-ME)/??
The same William Paul who's done nothing of note so far except a DUI? Also, guys like Rand and probably Amash won't be Libertarian nominees. They're in the Republican party, so I find a switch less than probable, although certainly not impossible. Another thing: Jesse Ventura just endorsed Bernie Sanders, he's not, by any stretch of the imagination, a Constitution Party guy.
This applies to everyone: keep age in mind. I know it's tricky, but make sure the future names are fairly young people. Someone who's about 60 now probably isn't going to be running several years into the future.