I think it really comes down to how well the new semantics fit the problem domain. If it's a much better fit than the alternative, it's a net win. But just because you can define new semantics, doesn't make it a good idea.

This is Nathan Marz we're talking about though; he's on the short list of people who can both accurately identify the need and create something workable to fill it. If he told me it was necessary for a particular problem domain, I (personally) would think long and hard before I disagreed.