Hi Patrick,
Great idea! I like how the new architecture framework helps separating all DSMLs, to reduce the interference. It's much more reliable, and makes it easier for users too.
The main issue I've had on the toolsmith side is that it may be complex to import the required dependencies (Typically, referencing element types or palettes from the architecture model, especially when you want to reuse Papyrus/UML ones, which are not necessarily present in your workspace). Playing with EMF's load resource and manually entering URIs is time consuming. Having some "Browse element type sets", "Browse palettes"... actions somewhere in the editor would definitely help! These actions should list all Palette/ElementType models in the target platform and/or installed plug-ins, to easily import/reference them.
Regarding the performances, there is a quite annoying issue in the Element Types editor, especially the first time you open an Element Type model. When you select an element, it can take up to a minute to load everything (After that, everything runs quickly, but the initial load can be really long)
I've had some other small issues here and there, but they are now mostly fixed in Oxygen.1
Cheers,
Camille