You should expect the same changes we had at 2.2. Essentially most things purchased with soldiery will be easier to purchase (because the cap is removed and supply slightly increased) as well as additions to soldiery purchased items (new crafting materials for ilvl 100-110 armor and infinitesimally better foods) Some items currently purchased with myth will be purchased with a reduced number of soldiery tomes (books, maps, etc.) and some items will be moved to GC (likely crafting items, with older crafting items seeing a price reduction). Myth purchased gear is already on allied seals and will likely stay there. Alternative level 90 gear will likely be introduced in the new dungeons (possibly the same old myth gear, but more likely something new).

New tomes will be rewarded anywhere you can currently get soldiery, though likely at a reduced rate with the new dungeons granting the most. New tomes will be exchanged for gear with an ilvl of at least 120, with upgrades to 130 available initially through coil drops. Coil gear will probably be 130 (135 for weapons) This will make SCoB gear less attractive, though still quite competitive for several weeks, until eventually it's more or less obsolete (as level 90 BCoB gear is now). Players seeking the best gear/ challenge will move on to the third and final coil of Bahamut.