This can't be done, as far as I can see. The existing route in core `GET /api/{v1|v2}/hosts/:id` will intercept this first, and attempt to look up a Host::Managed called "discovers" and fail:

    Host::Managed Load (0.2ms)  SELECT "hosts".* FROM "hosts" WHERE "hosts"."type" IN ('Host::Managed') AND "hosts"."name" = 'discovers' LIMIT 1

We can't change or override a core route from a plugin, routes are read from the top down. So I don't see how to do this - it'll have to stay as /api/v2/discovers for now.