National Wonders as Projects?

I think it would be a good idea if National Wonders could be build like a World Fair Project ... a project where every city can contribute ... in that way National Wonders would stay manageable even for wide empires ... otherwise if you go wide, you usually have to say GoodBye to the National Wonders which quickly become to expensive for one city to build ...

(In my current game on a huge earth map I am alone in North America but I dare not to settle more than 4-5 cities to not spoil the National Wonders ... what a waste of opportunity ...)

Some national wonders are a total loss in a very wide empire (hermitage + intelligence agency, at least). But the ones that matter (college and oxford) are easy to get. And oxford is better built in the industrial era anyway. Visitor's centre is worth buying hotels for in that marginal city you built in the snow for oil or uranium.

The other ones are all buildable after building useful business (barracks, monuments, markets, etc), so they aren't super hard to get.

The projects idea might be a fun mod. Alternatively you could just have the limit be "all cities or 4" or "all cities or total population of 50 or more". It makes no sense that (to use a US example) because you don't have a police station on Midway Island that you can't build an intelligence agency in DC.