Well we definitely know that what you're talking about is possible to a certain extent Safe-Keeper.  GD was able to setup a vanilla gunship to go spinning out of control if its engine was shot off, and I'm sure that could be replicated on our fighters, and other smaller craft.  As UnCo said, we plan on using this feature extensively on our capital ships as well, but all of this will probably come post-R1 as our coders are still working on basic functionality and balance at the moment.

I doubt that destructible-child objects will cause lag, they won't be adding any more polies as they'll just be parts that were already on the models.  The only problems I can think of would lie with their network code.

Yes, that's what I meant. Rather than a ship being one single object with one single physics code and hit points pool, you'll have several pieces, all with their own hit points and all interacting (staying together, changing the 'parent' when destroyed, and so on).