Would it be possible to give username priority first to sysops, then by number of accounts owned across different wikis, then most recent edit activity, and finally date of first registration? or some combination of these. That should reduce the number of conflicts to almost zero.

This would lead to conflict of values. We should be as technocratic as possible with all this stuff, then least 'value conflicts' can be raised. And sure, it can be implemented faster.

The best selector is most ancient revision actually (that nearly matches date of first registration).

Number of accounts on different wikis? Sure, there are people who register their accounts on every possible wiki.

Most recent edit activity? How does it relate to any sense?

Sysops? Should we encourage people to climb that ladder just because their accounts were safer? ;-)

Cheers, Domas