I think unlimited terrains need you to create a series of terrains over a grid like 3 x 3 or something, giving nine all told in this example, that will tile seamlessly with each other, then you would need to write a script to lock the Player in the centre of the map whilst everything else moved around Player when Player makes movement calls, ent_creating the terrains as needed and removing them as needed as well as the assetts they may contain.
This way you can have a few textures to add variety to the endlessly rolling terrain you have created.

Another way is to use Georges example from Aum series (forgoten which sorry) then when you need to, shift back to the center to continue.