The difference between tennis, where a ball has to go a specific side of a line every couple of seconds and football, where a ball might, if you're lucky, get kicked over a line half a dozen times in the space of 90 minutes is huge!
Surely this could be adequately covered with a camera or two? 5th umpire style. It works fine for cricket and of course Rugby.
The sooner they make use of all the TV feeds which are already available, and let the ref see (or be informed by) what the world plus dog have just seen, and screamed abuse at their TV set for, the better.