Under current rules they just needed to determine if he was a runner or not, that made or broke that catch. Because of his angle if they said he was going to the ground to make the catch (he instead lept after 3 steps) then he would have had to survive the ground as he was not yet a runner.
Both stood, which is likely how they'll need the write the rule. (or was Ertz confirmed?)
Replay should be designed for the plays where it is obvious that the outcome should change. The 80/20, 90/10 calls where it could go either way or it can be explained or leaned one direction or the other should yield to the call on the field.
That's a hard sell and will be just as confusing, IMO, in the age of 4k slow-mo and an easily accessible social media mob for any given side.
Cousin won $200 by Foles catching a TD... 40/1 odds, lol.