Forward passes should be about the easiest part of the game for technology to pick up.
To humans, who are terrible at judging perspective, forward passes are tough, but a computer program with a data base of how different vectors look from different angles should be able to tell if a pass is forward in close to real time.
We have programs that can land rockets remotely on Mars, and can guide missiles at hundreds of kilometres per hour to intercept other rockets, I'm sure calculating vectors in a small space at low speeds should be pretty easy.
It could even be used in general play, not just for tries. It won't, since no one will care enough to pay for it, but it should be easy, unlike most rules in league that have an element of subjectivity.
In the mean time (in the real world), I can't see why the video ref shouldn't be able to rule on anything that they can obviously see. Of course, we will dispute their judgement (quite rightly from the evidence of past performance), but that is not new.
If we were scared that video refs will make mistakes (and they do) we shouldn't have introduced them, and should get rid of them (as Gould argues). But if we are scared of increasing their powers as we fear they'll make mistakes, the other solution is to get better referees, or have even more of them and have them specialise in different areas.
There could be a referee who studies lots of videos of forward, flat, and backwards passes from lots of angles, and must pass some test on getting them right, and only rules on forward passes. At least every video referee should practice this and pass a test.
I just can't see how forward passes should be so hard to rule on with (ideally) proper technology or (less ideally but more realistically) proper training.