It's not just an engine change but a server restructure as well so they have to make sure our data is save correctly, etc. In an interview Yoshi mentioned it will take awhile, but he knows the community is there and wants to keep it that way.

As for if it's worth it I think 2 months is enough time to get a few things done. You probably can enjoy some of the current story line before it's gone depending on your playtime. I've read sometime late september and early october as when beta starts and that's when 1.x server will go down too. Here's to hoping it's only one month or less!