First of all, this is VERY aproximate. I doubt FFG will use this kind of formula to do their ships, they will just do them the size they feel apropiate.

But, for the sake of using math, I have done this sliding scale for the ships. It only takes in account the length of the ship. Using the size of the Victory, Nebulon B and Corvette, these are the different scales (and sizes) that each ship of the Star Wars universe should have.

This would be better if I had more ships to confirm the scale (like the Imperial Star Destroyer). Also, I doubt they will do the SSD Executor as just a 18cm ship. And this scale obviously doesnt work for fighters or smaller ships than the Medium Transport. So take it with a grain of salt. This (or a revised version of this) will be the forumla I will use to do my custom 3D printed ships

https://community.fantasyflightgames.com/index.php?/topic/138391-isd-base-size/

ISD estimated to come in at around 20 - 23cm long. Which im afraid blows your scale quite out, and shows why there would be significant issues with bringing the Executor into the game when the ISD is already that big. (In fact, even at twice the length of the ISD model estimate, the Executor model would actually be thinner than the ISD model, due to its extreme dagger shape - which would just be rediculous).

I would nott underestimate FFG...So far their track record of never is more like : At least nott yet...Adds more mystery to what they will release next..