What the wonders do will depend on mechanics, and game balance overarching policies on what abilities to dispense for hammer investment.
Wonder mechanics, I think have been played out in the "first person to finish gets everything" department. It was something to try and people don't like it, so try something else.
I would like to see the idea that when you start a wonder you don't pick the wonder yet; instead, you merely "build a cultural marvel" - something that you are permitted to do by meeting conditions. You know how Vox Populi and Civ VI each had ways of hiding the very ability to try a wonder behind a certain condition? And the total number of wonders you could have is limited? Anything that works like that could be in place, to allow you to try to "build a cultural marvel".
When you finish the cultural marvel, you get one. It does something worthwhile domestically and for your cultural heritage. But some sort of mechanic makes the construction "turn out to be" what we call a World Wonder. You build a cultural marvel in the 1800s, you meet the prereqs for Big Ben, bam, it's Big Ben. Naturally, some way to erase any random aspect is needed.
Let's examine this. The idea that people start building something without knowing what it is is, frankly, Fantasy. On the other hand, the idea that something might be built as a Monumental Structure or for a very specific purpose and turn out to have a very different effect is much easier to envision and justify.
So, I agree with the idea that you choose a 'Type' of Wonderous Cultural Structure. And the requirements for each such Structure are very specific: what 'allows' you to build, say, the Parthenon in the Classical Era may not allow you to build the Temple of Pythian Appollo (Oracle) or the Yellow Crane Tower. Each should also have slightly different characteristics/bonuses.
BUT As you progress, the effects of Wonders should change. Nobody's trying to plant a God/King inside a Pyramid any more, or mobilize a few thousand farmers between the planting and the harvest to build anything - the original characteristics simply don't apply. Yet the Pyramids are still a Cultural/National symbol of Egypt and a major source of Tourism - and Tourism Money, to the point that the tourism becomes a target for anti-government terrorists.
Even more extreme, the Long Wall/Great Wall as a Wonder would originally have defensive/military and possibly Trade (as in controlling it for taxation purposes) purposes/characteristics, but by the Modern Era and later - none of those really apply and in fact it would be hard to see where it has any effect in any of those areas, but is certainly still a Wonderous Structure.
2. Do we want to bring back National Wonders?
A bonus you can only get one of in the empire? Sure. A system that constrains expansion and development along an arbitrary timeline as a result of an extremely overcentralizing, overpowered, early game example of the kind? God no.
Completely Agree - at least, to bring them back in the Civ V form, completely agree. I think IF some kind of National Wonder mechanism was added (back) to the game in Civ VII, they should take the form of Wonderous Buildings, replacing a normal building with a less-than-game-changing set of extra bonuses and, potentially, later Tourism/Cultural or other effects (and giving us an excuse for more Graphic variety on the game map). For example, Rome's
Cloaca Maxima might be a Wonderous Sewer, Greece/Athen's
Lyceum a Wonderous Library, and later in the game, the option to replace your original Palace with a Wonderous Palace (
Buckingham, Topkapi, Schönbrunn, Tuileries, etc) would be a good way to 'use up' a whole bunch of would-be World Wonders on the list without turning the game into a Wonders Я Us construction frenzy . . .
I'm surprised we didn't get a dam wonder in GS.
Well, they had already bungled an early Irrigation/Food/Flood Control Dam Wonder by using the fake Great Bath instead of the
Great Dam of Mar'ib, but after that, yeah, there are a host of great Hydroelectric or Flood Control/Food dams available from the Modern Era on:
Boulder/Hoover, Grand Coulee, Three Gorges, Itaipu, Aswan . . .