That doesn't sound like it'd be difficult to map to the DNS. Something like a record per mapping with each record containing a pattern and a template ought to work -- where does it get difficult?
On another slightly relevant note, from the perspective of linked data and the semantic web, the <link> tag or "Link" header (both which are suggested by Google and URX) is meant precisely for this kind of reason: being able to link separate resources with a given relation (e.g. "alternate") who may have varying display/device/media qualities (e.g. media queries). Because semantic linkage is between two nodes of the web graph rather than DNS (which I guess would be a subgraph of the web?), one is able to use semantic metadata such as http://schema.org/docs/actions.html to describe not only how to access/consume a resource, but also alternate ways to do so (e.g. from an Android device instead of a desktop client).
Again the above isn't completely impossible to do with DNS, I'll give you that, but it simply is less tenable to assume template-like qualities of all URIs or to ignore the semantic implications of redefining how linked data has worked for the last decades.