MultiModel - code review

[amielsaa]

Hi Lars,

Me and Gil have been working on multi-model features and we encountered some design dilemmas, It would be great if you could review it.
As there are a lot of additions made by us, we made a document that gives context regarding the changes we made and what problems have occurred.
Sorry in advance for the length of the file but it will help us understand if we're in the right direction.

https://docs.google.com/document/d/1dqrV1VB6t9QIuCuwomYWxzgwsUelJkM169B01zVQJcU/edit

Thanks!