I expect them to sell the DLC maps separately. The thing about the season pass is probably for pre orders.
The PS4 exclusive maps will probably come to XBO and PC. I remember when they released MWR standalone and it was only for PS4 for a month but they eventually announced the Xbox and PC version.
They already said they won't sell the DLC maps separately and even if they backtrack on this, it won't be until long after the maps are out.
Even if they do release the BO3 maps for XB1/PC, locking them behind digital pre-orders was already bad enough by itself.