But wouldn't that also require a whole movie to do? In contrast, doing the whole All Star Superman test tube baby thing would only be a small part of this already altered Reign of the Supermen movie. It seems less economical, and positioned to sell less than coupling it with Reign, in my opinion. I imagine the DC animated film department goes with the sure bet more often than not. I mean, that's why they're doing Death of Superman again, right?
Story-wise that also makes Clark and Lois a full decade older than the other characters in the DC animated movies, and explaining Jon's existence becomes "the spent 10 years on Brainiac's ship where time moved more slowly and they had a kid a raised him till Superman found a way out." As opposed to "he was created by Cadmus (or N.O.W.H.E.R.E. if they like) using Lois and Clark's DNA."
It's by no means impossible that they might go this way, but I personally find it less likely given the DC animated film department's penchant for streamlining whenever possible.