These are great for the end game, but I think it would be better if the requirements were more around 8-10 thousand infrastructure. That way the requirements are still very high and above most nations with in wonder range (which starts at about 4-5000 infra) but not out of reach of all but a very select handful of nations.
For reference:
Nations at 14,999.99 infra or above = 2
Nations at 12,999.99 infra or above = 15
Nations at 11,999.99 infra or above = 30
Nations at 9,999.99 infra or above = 135
Nations at 8,999.99 infra or above = 278
Nations at 7,999.99 infra or above = 611
Nations at 4,999.99 infra or above = 4,153
Nations at 3,999.99 infra or above = 5,879
Disclaimer: This isn't just me wanting to get these wonders, even at 8-10 thousand infra I'd be way short, since I'm only at 5289.99 infra and have 4 wonders and started buying them at 3999.99.