As a Brit, I always merge early due to the sense of fairness. However, this is strongly enforced by the nature of road signs, which show, say 500m ahead, a diagram with an arrow on the right merging to the left.
All it would take would be a consistent change of sign showing merging in turn at lane-merge to change this behaviour
The odd thing is that you do see very occasional zip-merge signs in the UK, which tend to reinforce the idea that zip-merge should any be used in exceptional circumstance.
As someone who lives in Ontario, Canada, I merge early as a defensive/safety measure.
People here will follow each other incredibly closely, even at high speeds, and quite often they won't slow down to let you in if you're trying to merge.
All it would take would be a consistent change of sign showing merging in turn at lane-merge to change this behaviour