IN my opinion the modern era, or perhaps what we shall call "the late game" has two competing things going on.
1) It's near the end of the game and as a game, victory must be in sight
2) The game is in part a simulation, and you need to maintain some degree of that throughout all stages of the game.
With GS they addressed some of point 1. We got several game ending mechanisms, things to help get you to victory; rock bands, future era cards, the GDR for domination, etc.
However, the new power system and railroads, which partly point to #2, didn't really get integrated enough into how your empire runs. What's fun about Civ6 on the internal front is building and planning districts, improvements, and wonders. This puzzle largely dries up after the industrial because everything is placed, you just get more yields. There's no ability to change what has already been placed. There is no facet except more yields.
Yes, there is renewable power, and some water based improvements, but flood barriers solve Co2. And seasteads come in the future era, very late.
When we look at various proposals around corporations, for example, we see a problem in search of a solution: why would I want to go secure resources just to get more yields? There is no shortage of yields. Contrast to civ5's ideologies - several game systems were reworked so that ideological play was critical to securing a victory, be it tourism, science, domination, etc. So you need existing game rules either be changed or taken into account so that the solution to late game tedium, which targets #2, is compliant with the need for #1.
There is no reason, for example, that one could not rebalance things so that the late game gold or amenity situation was very difficult, and the penalties for failing here severe, and then create a corporation or ideology system that adds a degree of gameplay into solving those problems. You need the Chimera before introducing Bellerophon.
Personally, I would probably figure out how to add enough infrastructure/empire management changes and content that make the modern+ eras give the same type of challenge but in a new way, to keep me busy tweaking, planning, and improving my empire until the rockets launch to alpha centauri. Sitting around and piling up science just to unlock that last spaceship tech is extremely un fun.