There is a very basic plugin to do this already:
I would like to recommend this functionality be built in to WordPress itself, where all you would have to do is just choose the parent theme from a drop down of installed themes, give your theme a name, and poof! Instant child theme!
For maybe possible features: Option to either clone standard page (ie: single.php, index.php) or ability to create your own blank page templates on the fly in wordpress dashboard. (ie : myblankpagetemplate.php)