Originally I wanted to suggest to adopt #322 instead, but after I checked API I do not want anymore (ViewModels API is a hell, you can't just pass ViewModel factory as a lambda).

But my suggestion is still to apply its approach regarding ViewModelStoreOwner. I do not like that and how we moved ID management from Node itself to BuildParams. So instead, what do you think if we make it in the same way as ViewModelStoreOwner – provide RetainedInstanceStore API only directly from Node and not outside. We can capture all required parameters in Builder and pass them as a lamda to Node. From the first look it worse, but it is a good opportunity to 1) to do less potential API breaking changes now and in the future, we can always to go from inside-node approach to outside-node approach (but not other way) 2) check if direct dependency injection makes sense (partially dropping Builder and completly Interactor class as it won't have access to the feature anymore).

Would like to invite more people to discuss.

@CherryPerry I'm happy if we can come up with another solution. This PR allows Devs to retained objects within the builder which is useful of you're using MVICore.

The ViewModel approach in the other PR doesn't seem to have this functionality.

Perhaps we could support both? As devs using the builder/interactor approach need a solution as well