We know pretty much for a fact were going to Falinesti by now and now you're wondering how or why we would go to Mephala's Realm. So fargrave you have to remember the devs said they wanted it to be a central hub in the future and adding more portals to different zones. In the wiki of Falinesti it says and I quote
"in an attempt to bring the walking city back, the Altmer mage, Farandare built standing stones in the center of the basin to channel Oblivion, leaving cracks between the two realms."
Clearly this is where Fargrave comes in at connecting the 2 realms back together for us to portal between planes of oblivion. Now why Mephala ? The picture of the pieces these content creators got has what appears to be Mephala crown but not only that. During the 2 era which is what era ESO is in the wiki says "A lost temple to Mephala was uncovered by the Falinesti Faithful at the lost city's autumn resting site. you see that Autumn. We have 4 Autumn trees. Case closed.