I fully agree with you. Devs would be well advised to leave room for future modding by the community, by not only avoiding to lock knwon "entry points" to the Unity 3D engine, but also by foreseeing imaginative ways to mod their game around the engine... in the future.

For you may have missed one little point (or it's not so clear in OP): at the moment, there is no game, there are no updates, and there are no mods, at least not in the sense you seem to have in mind.

There is a early access game, more like an open beta/gamma test if you want.

There is a lot of work in progress, advancement is relatively slow, and saved games and mods are bound to be broken one day or another, several times before release.

There are mods at this stage only thanks to the game using the well known Unity 3D engine. Would the game use its own WIP engine, there would certainly be less mods around (only modders that can decompile the game or hack libraries, essentially).

So, I'd kindly say: post again 6 months before announced game's release.