I saw this a long time ago but since it got bumped...
Every variable exposed has to be networked to all clients which will really be bad for every canvas to have these features.
Having a scale for the texture is something I want to do (adds one vector variable), adding transparency support to cubes is possible (already a variable just not exposed).
Multi image support would have to be networked as a single canvas per side, which could be overdoing it, but could be investigated. Each canvas is a block of data containing a string (url).
As for dynamic patterning, that's probably not gonna happen.
I'd try to keep the side selection simple to reduce networking more variables as well.
Canvas Wall is something I will be working on soonish.