Dear Rhye,
I understand that you have two pages of requests to be included in the new patch and only one week to finish it all. I also realize that you don't like lots of drastic changes to your masterpiece
However I would ask all us to rethink few UHVs before the releaze of the new patch. Main motivation of the proposed amendments is to set deadlines every time there is a requirement to do something. That will make game more historical, will kill lots of exploits and will make it more challenging game. Also UHVs will look more consistent -- every single one with a deadline (certain date or before certain tech discovered) or the requirement to be the first. It also will require some luck and will require new strategies.
Here is the list of "no deadline" UHVs:
Rome
Build 5 Barracks, 5 Aqueducts and 5 Amphitheaters
Why don't set a date? If 70 AD is too early one could set the same 450 AD. It also will speed up the code, so no need to check every turn if there are 5 of each. Make one check at 450 AD and we done. Don't you think?
Vikings
Sink 25 ships
Uhmm... Tricky one... Not that many ships available to be sunk until the end of the Vikings Ages. Still can be 1500 AD though...
Arabia
Spread Islam to 40% + by the end of historical Turkish conquest (Vienna, 1683) or before discovery of the scientific method by any civilization.
Khmer
Spread Buddhism to 30% + before discovery of the scientific method by any civilization (how much this may slower down the Python code? One can set the date of Indochina's colonization otherwise)
Portugal
Found 13 extra-European colonies + by 1600 AD
Mongolia
Raze at least 7 cities -- This one is my least favorite in entire game. Even city size 1 is counted as city

And no deadline? What is the chalenge? If you ignore any other suggestion please review this one more time. So:
Raze at least 7 cities --> Raze 7 civilization's starting locations (Much more historical, will force more wars with more civs, will force to invade Russia and Europe). Also needs a deadline... 1600 AD is doable I hope...
Mongols razed Jin's Dadu and THEN built Khanbalik, razed Kiev, razed Samarkand, razed Baghdad. Tamerlain can be count as a Mongol, he raized Sarai...
Aztecs
* Enslave 5 European units -- By the time America comes into play. It may force Aztecs to go hunt those europeans
So this is it. Not that many to make UHV list more consistent.