I didn't want to post anything before you responded Niara as to not dogpile and also in case my information was outdated, but that also struck me as the opposite of what Loviatar is about -- Loviatar in many ways represents the opposite of what I'd think of as a healthy bdsm practice would be. A Loviataran is the kind of person who'd care about your limits and don'ts only so they can abuse them to hurt you even more. Loviatarans don't want you do die because when you die the suffering stops. But I'd much more expect them to want to leave marks, scars, chronic damage and similar (including emotional scars because they are equally into mental anguish and suffering) just because they know every time you hurt it will bring back memories of the suffering.
I get where you're coming from, but my view is that any way that they harm a supplicant, in which they will not make a full recovery from, is thereby one way that you cannot harm them again. You could destroy one of their eyes, but do it twice and then you won't be able to inflict that suffering on them ever again. Suffering without actual debilitation is important, in that regard.
I think with the current information we have, it comes down to different sects and how they individually practice - there will be some enclaves that practice closer to my envisioning of it (that's how it's always been portrayed in games I've played in where her clergy have shown up), and there will definitely be others that are more overtly destructive.
I feel that the main way in which Illmater followers and Loviatar followers differ is not in the practice, as it is the purpose and the feelings evoked. Loviatans draw pleasure, ecstacy even, from the acts of giving and receiving pain - pain is personal and intimate, and it exemplifies being alive. Illmater, on the other hand, views pain only as suffering; pain is a negative, which it is noble to shoulder the burden of, for the sake of others. One views pain as intrinsically good, while the other views it as intrinsically bad, and that is where they clash.
As far as I understand, Sharess is all about sensual fulfillment, and is inherently a pleasure goddess, and I'd certainly not mind spending a sojourn getting caught up in the endless revel if it passes by my town... but I'd not expect to find any, if many, practicing masochists in her ranks.
Still, I'm happy to admit I likely have a personal and experiential bias on this one, and may be seeing what I want to see a little bit too much.
