.htm for Mini Mobile and .html for aLL eLse Larger?

2014 might not be too late to achieve this simple option:

  htM for Mobile web content

  htmL for Laptop and aLL other Layout

Luckily, we never had an "xhtml" file extention - and we were permitted both SHTM and SHTML for server-side includes.

The reason to consider HTM for mini displays is that it would not require typing by users to shorten or lengthen the extension if browsers would agree on a hot-key combination.  A smart browser would check at any site offering an HTML whether there was an HTM if the last URL used was HTM by user choice and so offer the option visually to the user for the current site.  It would be a simple browser  configuration option for those devices, the format of which, was neither Large nor Mini.

Lately I have been using htm for 4.01 HTML and html for XHTML and also for HTML5.  As the web moves to the latter, we should be able to set a meta value to flag that, say,  this .html file has a sibling .htm file for constrained display and vice versa.  And ditto for .shtm and .shtml and whatever might follow from 2014 until we achieve 20/20 hindsight.