One action/template per form/step?
Yes, that's easy if you hard code your templates.
I needed solution for forms with fields 'generated' by user in runtime.
Since then I've coded a module for that.
As the module was coded for specific requirements of my app I'm not going to release as plugin or snippet - the module ties too much with the app core code.
I'm thinking, however, how to make it more generic and then do a plugin.