The core team indicated they quite like the sequential numbering that SVN gives them. I'm considering building it into GitLab as an option if they would use it to host ruby :)
I personally never like the meaningless hashes. Those numbers act as good identifier of project size and progress. It quickly shows what kind of ranges we're taking when doing a compare, or simply looking at files and seeing those numbers.
It gives a lot of context. Just look how much more useful information a compare shows r1808:39334bf35fdf...r1819:3e8df3a82397 vs 39334bf35fdf...3e8df3a82397
Would you implement it using tags?