I would be happy if you just add an option that incoming connection goes out via the same interface it came in, regardless of other routing settings.There is no method which "just works". Something will still need to be configured, either PCC or Bonding or something else.
I guess we all thought that when we first met with Mikrotik routers.I just have to say these mikrotik routers are friggin awesome! The features, the management software, everything. Great job to everyone at mikrotik!!!