Earlier quoted context omitted.
I think that's a really great idea, too. The worrisome bit around constraint solvers is that they're really easy to get into strange "spooky action at a distance" states of constraint interaction which are incredibly tough to escape from. Building good constraints thus feels like something of a black art.
Sticking to Newtonian rather than using quantum physics can avoid the spooky action at a distance problem (I know this isn't what you meant, but I couldn't resist). Actually, constraints are quite explicit compared to imperative assignments.
I believe that constraints are explicit, but their cumulative effect is difficult to predict. A constraint which wipes out some part of the feasible space with lots of vertices can have sudden and dramatic (non-local) impact on the solution. If your solver is approximate or your solution non-linear it might be incredibly difficult to figure out where the solver will ultimately land.