"When it's ready and not before" is the only answer you'll get to that. I recall someone mentioning that XFree86 4.0 might be ready by the end of the year, but that was unofficial (there is no 'official') and certainly couldn't be relied on. So, no, don't skip any upgrades waiting for something in particular. You could be waiting months.

Any idea how long these things take?

Should I skip the 6.2 upgrade and wait for 6.3?

...

First snapshot appeared a few days ago, labelled 3.9.xx. Obviously still Alpha stuff and not for regular users, but encouraging nevertheless.