I don't think that a 'new' type of tree settlement is necessary; according to the lore and the characteristics of this special faction, the Mallorn trees are the heart and the main element of the enchanted Golden Wood, being at the same time houses, defensive towers, palaces and other structures.
That's why I appreciated very much the choice of the Edain Team of having made the main Tree House of the settlement the heart and the centre of the settlement itself, where you can buy upgrades, recruit simple and 'advanced' units, alongside the heroes of this realm.
This is how Lothlórien works; it's not a 'common' region, like the territories of Gondor or Rohan, where you can build or expand freely; the Golden Wood is a 'magic', protected and watchful realm, with definite borders
Instead of defensive towers or 'walls', I personally would prefer more to find a way to tie the defense of the settlement to the power of Nenya and Galadriel