Will the mage tower even be a thing on remix?

Even without appearances…?

Idk prob not, power scaling would be weird. You can do a timewalking version currently live on retail though for a recolored tomb of sargeras transmog set. The guardian druid one also gives the fel werebear.

it will not. it was a one-time thing.

No, it would defeat the purpose. the actual fights are 6-7 minutes when balanced.
What would be the point?

The Tower itself? Likely. Each of the Buildings has benefits. It’ll be interesting to see how they handle the contribution mechanic however.

The Challenges for the Artifact looks? No.

Do we have everything datamined from Legion Remix, or they can still add new things for the next 2 phases?

If so, maybe they can pull the Mage Tower back but add some other reward into it.

All the raids / dungeons / content already exist, the only thing that isn’t available currently is the Housing vendor. All items on vendors through the end of remix are already there unless they decide to patch something in.