Just because it’s a unity game doesn’t mean it’ll be easily moddable, nor am I aware of any especially easy way to make it so. High moddability generally means setting out with a certain kind of architecture in mind, which Unity neither encourages or prevents. Look at KSP modding for an example, where unity experince might help with the super deep systems mods, but just throwing together some parts is a case of modeling and scripting just like a homeworld mod might be.
Also, even if it is highly moddable and made with a philosophy similar to HW’s, don’t expect to make spacegame mods easily. Movement for ground and space RTSs are different in some pretty basic ways that are unlikely to be easily modified unless they go really crazy with mod functionality, and even then it’ll be a great deal of work to get everything working very well.