Context subdomains

My idea is to provide a simple way to create subdomains using contexts. The setup would look like this:
* Multiple domains point to one drupal installation with a single site.
* Some contexts are defined that should show in their own subdomain.
* All links pointing to content in one of this subdomain contexts should be altered to point to that subdomain.

A simple example would be:
/node/A - does not belong to any context
/node/B - belongs to a context with the subdomain "context-B"

If http://subdomain.example.com/node/A contains a link to /node/B it should be rewritten to point to http://context-B.example.com/node/B

I am already familiar with context, spaces, purl, … but there does not seem to be a simple way to implement this functionality with those modules. [Please correct me if I'm wrong]

So I propose to write a module that simply uses url_alter to rewrite outbound URLs according to a new kid of context reaction ("subdomain").

Is there already a straight forward way to accomplish this using existing modules?
Would it make sense to generalize the proposed functionality to cover a wider set of applications?

Thanks for any suggestions!