I would want to bridge or clone two Matrix servers, one located in a intranet and the other in internet. Intranet can access internet (with not infrequent cuts) but cannot be accessed from internet. Both server are connected by a VPN so they can communicate each other.
Many of the users connect from the intranet and other from internet. The goal is that the intranet users can connect without going to internet, because the internet connection is metered and long periods without no internet connection are frequent. Ideally both servers would act as a unique Matrix server, so intranet users don't need to create two accounts. Servers should synchronize events whenever the internet connection is working.
I suppose this is not feasible without a quite big chunk of code. My doubt is which pieces of software should I create. Should I develop a bridge? Perhaps a bot approach or account linking? Any more suitable solution I am not aware of?