First, kudos to the dev team for the nice work on the mesh editor. It has become a game in itself i can't stop playing with. :)
A very nice addition would be a "Slope" tool... Sorry i can't remember the proper term in english, so here is a picture :

The deformation tool is awesome, but based on curve deformation. You can't transform a flat block to a slope with it (or a diagonal), because it will create flat tangents at each end. And correcting the angle will break the vertical faces. The only way is that "Slope tool" (correct me if i'm wrong).
That would allow a whole lot of block variations.
Please. :)
Also, a "Paste in place" option would be really useful. At the moment, even with large snap spacing, pasting a mesh from one layer to another is a pain : getting the 3 axes lighted is already difficult, but it doesn't mean the copy will be at the same coordinates, at all (maybe it's buggy ?).
Layers are great, they would be really awesome with a Paste in place option : isolate a part, work on it, stay aligned, etc...
Please, again.