Hello Pascal
Yes, a router can indeed serve two roles, as an MC and a BR. In a PfR environment, the MC and BR can be on the same router. This is particularly common in smaller network deployments where there are only two routers as you suggest.
In a two-router setup, one router can be set up as both the MC and a BR, while the other router can be set up as a BR.
Keep in mind that while this is possible, it may not be the best solution for larger networks due to potential performance issues. The dual role of MC and BR can put a significant load on a single router in a larger network environment. In such a case, it is preferrable to give different routers these roles.
I hope this has been helpful!
Laz