Th foil just keeps the juices from running away which I use to make the brisket even more tasty . I think the key is just keeping warm and letting the beef do it's thing . But WTF do I know really . I have cut that beast open right off the smoker and it was divine .
The foil steams the bark - white I like a little crispier personally ...
A drip pan under the rack will still allow the meat to do it's thing in an insulated space, and provide the juices, and keep the bark a little nicer ...
Again, though, it's a relatively minor detail and that looks good!