I think Teleportation fits perfectly in with Defiant lore, but not so much with Guardians, however, you cannot have such lopsided advantages for one faction but not the other...there would be no one to pvp against! So maybe shrines (1 per zone) made of pure sourcestone, and you have to find or craft a sourcestone fragment and attune it to each zone' shrine.
One of the most undeniably cool things to have is flying mounts, properly implemented though, I liked the Vanguard approach with the griffons and later coin mounts, and should be an element of gameplay, that is incredibly immersive. Perhaps Flying mounts only available from really tough Air rifts, but the other rifts having other specialized mount rewards. Of course, this could lead to mounted combat, and that is obviously something for after the game goes gold, in the first expansion perhaps.
ships are cool too, perhaps faction rewards for pvp achievements, for landing parties in enemy territories, but persistant, and usable for storage, housing, et. cetera. Again, stuff for the first expansion.
My two cents