This is blocked on migrating text from squid to varnish which is likely at least a few months off. Until then, MobileFrontend needs to continue supporting the current production reality.
Asher, thanks for the response. I didn't realize the functionality was so crucial. I'll go ahead and add it back in for now - however I'll probably slightly change how things work so the functionality in mobileRedirect.php is included in the extension itself.