CIS-2014 in Minsk.

A mirrored Jebus Cross exists — but it hasn't caught on, and it's unlikely to take root due to objective reasons

Can you name even one reason? Besides the fact that L-size is too large for the template, and no one has made adequate zone filling for M-size.

Hexagi has one external issue — 3 starting castles.

It is precisely the presence of multiple starting castles that allows for interesting gameplay under conditions of early contact. In fact, this is the main feature of this template family, not a problem.