Allow Mutable serializer to render templates?

It could be useful to return a data structure from a route handler and have it automatically serialized to JSON/XML or rendered in a template depending on Accept: header supplied by the user. Right now we have a Mutable serializer which chooses a serializer based on headers, but no way to render a template if user asks for text/html instead.

Mojolicious has respond_to helper which achieves this. Could Mutable serializer be extended to allow similar things? Right now it's not obvious how it would determine the template to render.

Feel free to point out the obvious solution I am missing, talk me out of returning HTML or JSON from the same route, or suggest alternative API designs. I can help with the implementation too, once there is consensus on how it should behave.

Start by reviewing the Mutable serializer behavior for Accept headers and the linked Mojolicious respond_to helper. The issue does not identify files or tests; the work is done when the project has agreed on an API and clear template-selection behavior for HTML alongside JSON/XML responses.