Attached is a patch that I've applied to cazfi.net server.
While this is not breaking things as such, I'd definitely would like to have it fixed before 3.0.0, so that it would not go in *after*. It would be rather big rule change to do mid-series.
Yet it's rather late to get it to 3.0.0-RC1 at this point. Patch submitted now would barely pass review period and would be pushed in only just before the release.
I looked back to 2.6.0 release time, and found out that back then we did some changes even between the last RC and the final 2.6.0 release. With that case in mind, my proposal is that we push fix to this (immediately) after 3.0.0-RC1.
Hex should be the default in freeciv-3.0 and later. Multiplayer ruleset is not one of the rulesets that should change that, but it does.