Please see Help_talk:Magic_words#Basename_without_filename_extension
Topic on Project:Support desk
Users should generally discuss feature requests before posting them at the Phabricator.
That's probably too niche for us to make it a MW core magic word.
You could create an extension, or you could use Extension:Scribunto (or parser functions with string functions enabled) to make something equivalent.
Try this: [[File:{{#explode:{{PAGENAME}}|.|-2}} 2.{{#explode:{{PAGENAME}}|.|-1}}]]