No, this is not possible, even as a concept it requires further refinement to avoid fundamental problems.
For example, if your child theme has a single.php
and WordPress tries to load page.php
, it will load the page.php
in the parent because it doesn't exist in the child theme.
But if we have multiple parent themes, which page.php
should it load? What if we solved that problem but all these parent themes were wildly different, which almost certainly means they'd be incompatible with styling issues and broken layouts. If they were similar enough to work together you might as well merge them into a single theme.
We could try defining a hierarchy and using grandparent themes, but that's also not possible without changes, and has serious problems and difficulties. For example, what if a theme is it's own grandparent?
What I suspect is that this idea is a solution you came up for another problem, and you're now asking how to do this rather than working on the original