apropos of nothing, i just imagined a network architecture in which traffic leaving the local broadcast domain would be initially multicasted, and then any of a set of routers sharing the broadcast domain could elect to route the traffic at which point it would switch to unicast
— Graviscera (@gravislizard) October 25, 2018
You don’t have to imagine this. It already exists. There are several ways to do this. VRRP combined with policy-based routing can do the equivalent of this and far more (though some of the terminology in the tweet is not really relevant) and several dynamic routing protocols such as OSPF will do this as well when combined with VRRP or another resiliency method. VRRP supports up to 255 routers, by the way, so go crazy if you wanna with routing things every which way.
There is also multicast BGP to use, if you need to go really wide.
This is a long-solved problem in networking, in other words.