Founder / project creator here. Ory Kratos has been in development since 2018 and is approaching version 1.0! If you have any questions about the project, tech, flows, or Ory as a whole I’m here to help :)
I do run Keycloak in a container but I'm pretty sure spinning up a new instance for every realm would be more resource intensive than using multiple realms in the same instance.
It's just a question of use case at the end of the day. In my use case I only need this for small internal tools so it's easier to just spin up one instance for me.
LE: I guess it's being tracked in this GitHub issue: https://github.com/ory/kratos/issues/274
not sure if that is everything.