League average for 30-39 yards has been around 90% over recent years.
But that includes odd angles. My guess at this year's percentage success will be 96-97% for the new extra points, but we'll see.
I agree weather now becomes a major factor in some games, but inclement weather might also effect success rates for 2 points conversions as well. It will be up to the coach to decide.
Knowing how conservative coaches are, I don't see this as some drastic change in the way the game will be played.
I think people are reading WAY to much into the decision.
In the 1970's (when they first moved the goalposts back), XP percentage was around 92%. That was the low (even lower than the 1960's). By the mid-80's it was in the 96-97% success rate. The last 5 seasons, it was over 99%.
Why can't the simplest answer be the truth? The league just wants the XP success rate to go back to about 95-97% and doesn't want to change the success rate of 2-point conversions (currently at about 47-48%).
The excitement part comes from those available percentages and the strategy they provide over the course of a whole season. There is no effort to increase 2-point tries (although that will likely be a small effect) or change the way the game is played or change the basic assumption a TD is 7 points (rather than a bunch of 6's and 8's).
Why not just try to get the XP try back to how it was in the 1980's?