I feel umpires call should go away for both DRS and on field calls. If you say DRS isn't perfect, then we know that it could be off a little if any, but umpire can be off by several inches as we have seen since forever. At least with DRS, the inaccuracy is same for everyone unlike in case of umpires where we see same umpire gives mistaken out sometimes and mistaken not-out sometimes and then each umpire is different as well. As for on field calls, umpires call doesn't make sense either. Where technology is not able to figure out even with the superfast/magnifying cameras with multiple replays, I can't see how umpires could even come close to that accuracy.