... can really be ...
... would be ...
... could be designed to ...

Apparently, Joint Database Technology is still a castle in the air, isn't it?

I don't see a single item in your argumentation that isn't very likely better (and /much/ better) done by an already existing system like PostgreSQL, which already exists(!), has been developed and improved on for 20+ years(!), and is standard-compliant like few other systems. There is a large community of people improving postgres, producing a new version (with new features) every year. Bugs often get fixed within 24 hours. PostgreSQL is completely free and you may use it to build a closed-source system.

Here is a challenge: can you publish here such a system of your design, giving full code, and using data in the form of free text files (or even self-generated ones), so that any one of us can reproduce it and test its performance? (multi-platform, please: windows-only is not good enough).

If you do that I'll try to counter it with a postgres-based system to parallel it. Only then can we see what are the pros and cons of your SDBM/hash/perl/text-system versus poor old conventional PostgreSQL.