Here is the quote from live letter III about the level cap:

[0:38:58]
Q: Are there any plans to increase the level cap? If so, when?
A: At the launch of A Realm Reborn, the level cap will still be 50. We're already planning to implement a lot of content specifically for level 50. If we decide to increase the level cap at the time of launch, we're going to have to implement additional content before we're able to launch ARR.

The current plan is to increase the level cap with the next major update after launch. We will also be updating the content to reflect the increase in level cap. So the level cap increase will happen. It just won't be happening at the launch.

Unfortunately, I'm not able to give you a time frame on when it will occur. Please note that the battle system is completely different in ARR, so even if your character is already at level 50, there's a lot to re-learn.
So It doesn't directly say patch like I thought it did, but they have already been clearly thinking about it. I don't think "Next major update" means expansion though. I am pretty sure this is on his radar as of now and may have been pushed back to get some more important things into 2.1.