I measured a 2% slow down in the SimpleValidation benchmark when reintroducing isConstrained(). This is the worst case scenario as the validation is very simple but it's still something.

I would vote for keeping it the current way and remove UnconstrainedEntityMetaDataSingleton, especially considering it's useless on WildFly.

This, if we can get to the point where the memory footprint of an unconstrained bean is minimal (see https://hibernate.atlassian.net/browse/HV-1447).