The way I envision "pulping" is just a step beyond all-red damage is currently. For things that move under their own power, pulping shouldn't really have any effect when it happens, since a fully damaged limb is unusable.
I'm pretty sure that thralls aren't going to be any easier to deal with, since their whole deal seems to mainly be immunity to pain (which seems to afford an enormous advantage in combat), and if you can get a part fully damaged then it can't be used anyway, regardless of pulping.
The only place it ought to show up is with zombies, and perhaps material-based creatures, though once again, I would expect that mangling a bronze leg into a pulp wouldn't be easy to do (and I suppose "dusting" or "rubble-ing" might be better descriptors). The mechanic is (from what I understand) something to handle situations where the damage done to a part is extremely extensive, to the point where it seems strange that it can still be used by the creature.
What you should probably actually be worried about is how much HARDER the (proper non-thrall) undead are going to be in upcoming versions. Right now the fact they use hit points makes them very very easy to defeat. The pulping changes mean they are going to be moved back to the standard combat mechanics, but with some way to damage them beyond repair, but this will probably be very difficult to do. My expectation is that zombies are going to end up somewhat stronger than their living or husked counterparts, and that unless Toady does some reaction-timer stuff along with the combat mechanics, necromancers are going to be (even more) completely unstoppable.