That's a pretty good design, both in terms of function and legality.
I could see the RCMP calling it a bullpup (They've pulled that s**t before...), so if it cannot function with the buttplate removed, then it hampers that tactic.
Using 10/22 barrels might be worthwhile, as well. Then you can just sell the receiver minus the barrel
Does anyone manufacture aftermarket MkII or MkIII lowers?