Impossible to say. Right now, SEA is the junior 767 FO base, but the NGO - EHU trips were pulled right as it opened and MIA added cargo trips for Caribbean Airlines. MIA being the new hire 767 base is just as likely as SEA.

I imagine that when the company begins hiring, there will be enough movement off the 767 to create vacancies in MIA. You can fill out your standing bid by Indoc day 1 or day 2. Hopefully near-monthly vacancy bids return.

However, if you live in South Florida, you may have a better QOL being SEA based and bidding trips out of MIA, should they continue.