Behavior switching in YAML config

The following discussion from !9805 (closed) should be addressed:

• @grzesiek started a discussion: (+1 comment)

  We usually use Simplifible strategy to make it possible to simplify some configuration, and not to actually switch behavior completely. Perhaps we should have Bridge::Upstream and Bridge::Downstream, and a factory method, but I don't have a strong opinion about it.

We should explore the possibility of renaming Simplifiable or figuring a new way to implement behavior switching in the YAML config.