Multi PHP version aren't already supported in 7? I can use different PHP versions for different domain currently.
But i think it's more important to replace Qmail to Postfix, add support for clustering (mail, web, dns). In a bigger production, these things are very important. Qmail is a nightmare to debug when there are issues. It's config is a hell to be honest.
I've tested Klomo-MR with "slave", but it's not working properly.
Kloxo-MR 7.0 will be final release immediately. After that, will be release to version 7.5 with new features like real 'multiple webservers' (think like 'multiple php' where each domain use different php version).