There is no definite word from Sony on this. I agree that it's safe to assume that they won't be 1.50.
At the moment, it looks like Europe is going to get their own firmware. Like how 1.52 was released specifically for the US (new Japanese units still ship with 1.51 at this point, even though that may change at any time). So there might be a 1.53 by the time the PSP gets released in Europe.