It has been confirmed that mynook.ru also works for updating to 1.5. You do not need to change the packages.xml in your case, it already makes mynook.ru default.
That said, everything hinges on the update keeping the custom launcher, and if, for whatever reason it doesn't, being able to revert to 1.4.X by hard reset.
So far 2 people came out with not being able to go back to 1.4.X. If you are happy on 1.4.3 or absolutely need your Nook to be rooted right now, do not upgrade. Why take the chance?
If you do not really need to be rooted, can wait till a method to root 1.5 directly is available, really need the 1.5 features or trust that the reverting will bring you back to 1.4.X in case of a problem, then go ahead!
