We'd rather not mix episodes with each other, it'd just be prone to a lot of bugs.
It would take like 5 minutes to make a quest with just the bosses.
Else than that it would just be totally game breaking?
There would be no more good reason to farm TTF for RR, CCA for experience, RT/Seabed for PGF etc.
If you want to do that, you can play on the Test server and successively do /warpme 11, 12, 13, 14 in episode 1 for example. Don't even need a quest.