I can Click Add button below block to add a new block below

[MAX-786]

The location it appears doesn't seem related to where the add button is so that means we can do it on adminui side no problem

but just use the existing add menu. making it like the quanta one is out of scope

The add button should be bottom right outside, if the container is vertical.

But if the container is horizontal it should be top right outside since the added block would be to the right not underneath

Quanta doesn't show what happens when you have no blocks on the page. Probably the add should appear top right of the contents area but in the current api we don't know where the contents area is...
The other way to deal with this is always have at least one blank text area on the page. if the users deletes the last one, create another?