Schematics and Aetherium
Why? Why should large guilds be restricted? Because smaller guilds cant accumulate the manpower capable of producing donations?
When HoT was produced they made changes to reduce the effectiveness of large guilds, one of those was Aetherium production. This would simply continue that.
A really large guild could dominate a WvW fight with stuff bought via gold. That is one option but not necessarily the best if what you are after is ‘some good fights’. For many guilds Aetherium is now completely worthless, this change would give it value again.
It would restrict large guilds, but that is a potential restriction. It depends on pricing, it may be that a large guild can build as much as it used to but spend Aetherium rather than as much gold and mats.
If a medium guild is willing to put a higher amount of gold per member in they can produce at least as much. There are also guilds with members who have a lot of real life money and are willing to back their guilds with it.
They should fix the ridiculous pricing on some of the schematics instead slapping on more restrictions into the game.
Also your idea for restricting large guilds will also fail due to the multi guild system. If a guild actually had that much gold flowing around they could just get some members to create another guild and claim more guild halls and all of them would be producing aetherium in parallel. Now they have an even greater advantage.