I disagree with this entirely the whole guildwars model was built around “no subscription fee ever” and by adding something like they will cause a huge negative uproar to pretty much 90% of the community who are casual.
There are diminishing returns in place for a reason, if by giving select few who pay benefits to farm so much gold very quickly, which they would if given the chance it would completely destroy the economy, for example If the farmers pay this amount to farm all the time and get so much gold, the gold will slowly become less and less valuable and prices will rise on the trading post because people can just buy anything. Then there are the people without these privileges, struggling to ever keep up with the constant price rises and never being able to afford items they may want from the trading post.
It creates a divide which isn’t wanted or needed in guildwars.
You say how simple it is yet you haven’t even bothered thinking about the effects that it can have on the game in a whole, yes it may create revenue for anet, but they will also lose half of their playerbase in the process. which probably isn’t worth it.