I suspect Cryptic will ultimately follow something similar to Turbine's model of releasing "adventure packs". For example in DDO, Turbine generally releases 4 adventure packs every year. Subscribers and lifetime members automatically get all adventure packs unlocked so they don't have to pay for these adventure packs.
For F2P players, they generally get one adventure pack for free every year (typically in March, when the number of players are at an all-year low). The remaining three adventure packs, generally released just prior to major school breaks and major holidays, are locked and F2P players have to pay to get these adventure packs unlocked.