Comment 3 for bug 1646596

I think we might want to enforce that silos with development series targets (ie zesty) must be built against -proposed when this feature is implemented, to help guard against people building packages without, and then landing them. Compiler and library updates there tend to be more severe, and if not careful, landing things without building against -proposed can break migrations or end up in release earlier than they should while dependencies are sitting in -proposed.

Since there are many variables that determine when things get through -proposed, and not all packages have autopkgtests, or sufficient ones when they do, I'd be cautious to rely solely on proposed migration blocking things in the situation where one builds a silo without -proposed enabled.