I think it should be in game but it should be sent to players who have had 6-7 months of continuous subscription. Allowing people who have experienced the patch including the break between patches as well. Simply because the data would be skewed if you asked someone who just started the game 2 months before the patch when they didnt even experience the last patch.

In other words there needs to be conditions met before you ask players. And the poll should be 3 weeks- month after the launch of the patch. Giving players plenty of time to try out all the content in the patch.

However avoiding skewed data has to be a primary focus, otherwise the poll is pointless.