So I just watched yesterday's ESO live, and it looks really awesome and I can't wait to play and see Vvardenfell again, BUT, to put it clear and simple:
Telvanni Mushroom Towers are _NOT_ based on stone towers. They are grown. There are no stone stairs leading to the door, there is no stone floor inside, there are no stone walls, no stone at all I have ever seen in TES3 or Neloth's tower in TES5. There are stairs and winding paths, but it's evidently not made of stone.
Usually I am not a big lore nerd, but I am part of "The Great House Telvanni" RP/social guild, and many of our guildies are pretty much soaked in lore, specifically on the Great House Telvanni.
The towers are made from a special kind of Mushroom magically grown to become those towers. I don't think I even have to start lore ranting here, especially because I am not even very good with the details (I bet others will cover this soon...), but it takes a simple google search for "Telvanni Mushroom Tower" and a good look at all the pictures to see: NO STONE AT ALL. Or just get good old TES3 running and walk around in Sadrith Mora, or look at Tel Mithryn on Solstheim in TES5. I love the design and looks of the towers I saw on ESO live, which makes the stone base even more painfully to look at.
I guess my guildies are not the only ones who have waited to see Telvanni Towers in ESO. It's kind of the main attraction in the coming Chapter.