It's been a roller coaster while LL figures out prim equivalency. With people owning parcels with limited prim count, and mesh upload creating a seemingly heavy cost for even simple objects- it seems the mainstream use of mesh is going to be relegated to avatar attachments.
Ironically, this may cause a boost in Opensim/Aurora usage, since prim count is virtually a non-issue there. In some sense, you could suggest that it's easier/faster/cheaper to develop a plot of land in an open grid if prim equivalency cost keeps mesh from replacing sculpts in the architectural and landscaping arena in SL™.
We'll see how it pans out though. It may eventually end up that the cost/benefit ratio is acceptable enough. In which case, the next hurdle is to get everyone on a viewer that can see mesh.
Links for further reading:
Calculating "Prim Equivalency"
Prim Equivalence Explained