You can already add new model IDs, of objects and vehicles with the engineRequestModel function, I already suggested that to SAES in order to make a T-72B tank model based on the Rhino model (with all its sounds, etc) and leave the original Rhino model ID for an Abrams M1A2 for there to be two tanks.
Unfortunately SAES development team is like 99% inactive, they're only able to patch and fix things up so they're not gonna add things in the long term, I suggested a long time ago to Tut a model I slightly retextured for SAES to replace the Maverick vehicle with the Huey helicopter, and there was a military variant and a civilian variant, but devs don't care, plus you can't suggest vehicle replacements so he realized that and denied it and passed it to SAES and you know what the answer was, it was ignored, nobody from SAES DMed me back.
You have more chances to get suggestions done by the community's contributors aka Jord, Jonas, Infinity, and or Steven than SAES itself, but there is this thing, getting Nanobob's approval upon a "close" quality assurance review.. And that is a different thing.