Whatever the effect of the change, it would be greater if the distant regions can add up to a max of 20% for each res so why not?
This will create more wars, make big nations stronger and harm small nations but the effects are greatly muted if the distant regions can't add up.
PS: At no point here I am not saying that the changes are positive for the game, that's obviously not the case.
The only asset this game has is that it banks on patriotism/nationalism/xenofobia, w/e you want to call it. Differences in productivity are leading to mass migration and a dilution of that main asset.
Differences in productivity also harm small nations and favor big nations in a disproportionate way from an economic point of view.
In the old days it was much better, with a few iron regions fueling the wars but overall there wasn't this insane unbalance between big and smaller countries.
If you wanted a better game, you would get rid of differences in productivity ,allow everybody to go home and find a less harmful way to fuel wars.
The core mechanic here won't change. 2 or 10 distant regions with the same resource will still be 10%. Just like it was now with 20% bonus.