I think it would be more interesting if the Benelux was formed e.g. Customs Union first, with fuller political integration later - before the formation of the 'Common Market.
The Benelux I believe would have a similar language ratio spread as Switzerland does, and they seem to manage their internal diversity.
The Country would have more influence being a larger one, while the politicians would have less opportunity - only one government, not three.
Lets say it happens this way. Would it come close to France and/or Germany economically?
ASB I assume as countries merging or reforming tend to go there ,eg WI reunited Austro-HungaryWhat ASB or Pol?