The ability to buy off neutrals is just one of the points under discussion. It doesn't fundamentally change the game, and certainly doesn't affect the balance.

It does change it, and fundamentally at that. It might not affect the availability of use for both players ("balance," as you put it), but it radically affects the game itself — the tactics and strategies of all game components, including bidding for towns and color (even the bidding itself likely confuses some of the foreign audience). This innovation will require a review of many aspects and a new prioritization in games.
I'll repeat once more — if players from other countries and platforms find it problematic to adapt to any HeroesWorld rules, then changing any functionality will be an even bigger problem.
But, on the other hand, again — he who pays the piper calls the tune. If the goal of the tournament is to test certain ideas/innovations, then there are no questions. But then why bother with the World Championship?
You yourself say that the goal is to find an option optimal for a wide range of participants from different countries. And such an option, by your own words, is classic SoD under anarchy rules. So there's no need to change much (only bug fixes). Otherwise, it will no longer be SoD, but yet another amateur game addon that will scare off many potential participants.

You can create a bunch of addons for any game and try to run something there. But the official versions still remain — firstly, as the engine and common link for all subsequent addons, and secondly, they are the ones that will be considered the original, classic, and official versions. Whether someone likes it or not.