It's not really that it is a grave feature not to have, but would be a great feature to have. :) My poor laptop (Intel HD 4000) can't handle editing and preview rendering at the same time without locking up, so it would be really nice if Kdenlive could send the rendering to my desktop (GTX 295!) and let it do the grunt work without risking locking up my laptop and making me lose any unsaved changes.