A 156 and 320 (not a 321) could also signify the North Clyde, similar to what Thomson Interactive (who may or may not still have some association with Rivet) did for TSC. Except that had a grand total of about 6 scenarios for a commuter route where trains run every few minutes. 156 would essentially cover the WHL services from Glasgow Queen Street to Helensburgh Upper (for some reason they used a 158 in the TSC version) and also the Anniesland shuttle. Pure speculation of course and a bit of a stretch to see Rivet pulling off something as big as this route but more likely than the WHL IMHO.
I have just looked at the images again and the 156 PIS displays the text 'it's happening'. Of course that probably adds nothing interesting to the speculation but I didn't notice it at first. Edit: After thinking about that for a minute this seems rather strange, because why would they put this on here if it wasn't meant to be leaked, because everyone in Rivet would surely know it's coming. I may well be overthinking it here though.
I have been shown them yes but the person who has shown me them has asked me not to share them. I do know that the person who shared them with me is reading this thread so if he would be happy for me to put them on I would be more than happy to. I just don't want to get anyone in any sort of trouble.
No worries, if the person who showed them to you doesn't wish to share them with anyone else then that's completely fine, I don't want anyone getting into trouble.