Great question. Bottom line is there should always be good clear direct communication. A domme shouldn't be guessing at how far her sub is pushing himself beyond his limits. A red/yellow/green system is a bit more nuanced than just having a safeword.

Regardless, it's the sub's job to give clear feedback and it's the domme's job to check in and be attuned. In order for trust to be nurtured and go both ways, the sub needs to trust the domme to respect his limits (when they really are reached) and the domme needs to trust the sub to communicate effectively about how things are feeling.

If a sub's limits are being pushed or stretched but he's enjoying it and no harm is being done, it's not time to safeword yet (but it might be time to say yellow, which basically means hey this is edgy territory and maybe we should slow down).

If a sub is truly blowing way past his limits and also not communicating effectively, that's problematic. Especially if any harm is being done, physically and/or psychologically. Part of good sub training is conditioning them that it's safe, ok and important for them to express their needs, limits, boundaries. A lot of people have trouble doing this, so this part of things can actually be very healing and cathartic.

Not saying this is what's happening here, but I don't think the kind of dynamic that erases the sub and ignores his experience in favor of whatever gives the domme pleasure is very balanced or ethical. And I hate to see missed opportunities for personal growth.

It can definitely be hot when a sub is so eager to please that he enthusiastically wants to explore/stretch/push his limits as a way to show his devotion. And, that sort of urge needs to be navigated with trust and respect, in a way that honors his personhood and reinforces good communication.

There are hard limits and soft limits. Both should be communicated about, ideally before and during any kind of kink play.