I believe this would be a killer feature. The reason behind this is quite easy:
If you have routers (e.g. Mikrotik, Ubiquiti, …) in your network and you are using managed routes you are running risk that you are willy nilly change the routers config and that can have disastrous results, especially if we are talking about a remote router.
Routers and nodes just have different needs, wants and security as well as architecture requirements.
Simplest solution would be to be able to select alltogether if managed routes are delivered or not to a specific node. Of course the “deluxe” version would be to be able to select on a route and device basis which route gets delivered where.
I think that a simple implementation should be with rules engine. It would be great to extend the capable actions to add or not all or specific routes to certain circunstances IPv4 source address, etc.
I agree, every host can be set to non managed. At the same time though: This really goes against the brilliant idea of having all the information about a specific network in one pane of glass. Especially if the network that is being managed is more than a handful of systems, or god forbid very dissimilar with many different requirements having to manage this in every host by itself very quickly becomes a nightmare. I have shadowed routes in the past and effectively cut myself off. Much easier if I have all the routes that I am pushing (or not) in one place rather than 400 places