A few minutes of searching threads with multiple posts in the last week would show new hires getting the 756 in training frequently, and that class seniority for bidding fleet type goes by age. Have a look in those threads for more specific info. If not awarded in class could likely bid over in the first vacancy so long as you were ok with EWR.

Have heard no rumors of MCO expanding to include the 756 and would evaluate it as unlikely. The 756 pays about the same as the 73 (except for the 767-400) so if MCO is important just go to the 73.