The grassbump was originally created to be similair to the T2A landscape but it does it differently.
The T2A landscape uses mostly cliff tiles with grass on the edge to achieve the effect, where as the grassbump uses regular cliff tiles.
It wouldn't be that hard to include this into the next mod as it technically doesn't require a transition. The tile is the transition in this case, and it would just be a matter of painting it in the bmp.
As for the walkable transition, it's not really possible as-is in the grassbump, other than making a part of the grassbump color touch forest color. Of course then you get the 3-way transition that Dragon can't do. Either way, some manual tweaking is required.
As far as a walkable transition goes for the T2A way, I think you'd still end up having to manual tweak it. There's still a 3-way in there.
Where I've found the grassbump most useful is making a kind of maze type terrian. Like this:
Notice that it's surrounded by water. That's so there's no "external" cliff around the whole thing other than waht's normally made by the coastline. The part that is walkable is the forested area at the head of the rivers. No cliff there either. It uses the same transition as the regular grass when it comes to anything else, like forest or water.
Here's what it looks like in-game:
I hope that explains it a bit better. Also, put in a suggestion for any new colors (like forest-cliff) in the New Colortable thread. That way I don't forget it.
-Ryandor