Indeed, the tribute could have both the plexy or the saphire, and still be consistent with the original (standard or deluxe).
As much as I think it is important to have a plexy for the re-editions of the polaris or the Deep Sea (because domed plexy has a special shape and feel and is an important characteristic of the original watch, and the tribute is meant to be as faithful as possible to the original), I believe that for a flat surface and for an 'interpretation' as in the case of the reverso, I think that the practicallity of the saphire is more important (plexy doesn't add anything but worries on a flat surface).
So, let's see what the final watch looks like. Though both are 'right' from an historic perspective, I don't see the point in puting a plastic crystal on the tribute.