what 'knows' the HEAD?
Overall though I think a federated system that also handles issues is better, something more akin to Fossil.
However I think the main problem is almost always existing users. Git has arguably been falling behind in terms of features for quite a while now, but its momentum makes it hard for a lot of devs (including me!) to switch to a different vcs.
It’s all I’ve ever really used, and I’ve never seriously considered alternatives. What features in other VCSs are interesting?
All in all, I'd just like a distributed scm that doesn't feel like it was designed to make Linux with 10,000 other people. It is... frustratingly sophisticated at times.
GNU arch was an early DVCS but didn't seem to gain much traction. It was eventually superceded by Bazaar, which is much slower than git but was better at tracking history e.g. across renames. I think git has improved in that area, and bazaar has been getting less popular.
Fossil is built on an sqlite database and has a built-in Web UI and issue tracker, which is fine for those who want that but violates the "do one thing" principle (e.g. if you wanted to use some other issue tracker).
Darcs keeps track of patches and their dependencies, unlike git and mercurial (which track snapshots and their diffs). This approach supposedly makes life easier, and makes the darcs CLI quite usable. One problem is that some of the merge algorithms can take an exponential amount of time to complete, which has been getting addressed in recent years but many users seem to jump ship to git.
Pijul is similar to darcs, but breaks compatibility in order to solve the exponential merge problems. It looks very promising, but is still very new.
My projects aren't big enough to have their own sites, but I do push my repos to IPFS and give links at http://chriswarbo.net/projects/repos (actually using IPNS, which should reduce regeneration but is still experimental and flaky ;) )