We're excited to announce that we've fully migrated the Xbox Forums to their new home, here on the Microsoft Community forums!
As of today, going to forums.xbox.com will redirect you here to the Xbox area of the Community forums. We've moved all of your existing threads over so you can continue and start conversations with the new forums experience.
We sincerely appreciate the feedback you have provided over this transition and can't wait for you to check out the new Xbox Forums!
If you play the 360 version of Minecraft on a One, I can't see why it would not load the worlds you have now.
OTOH, if you are taking about Mojang making a XB One version of Minecraft, then it loading the old saves is entirely on Mojang and what Microsoft will permit them to do on the platform. Maybe it will. Maybe it won't. Have to wait and see. My gut feeling
is no, it will not. Microsoft says they will continue to support the 360 but they are making every effort to force everyone they can off it and onto the new console. So given that attitude, I doubt Microsoft wants developers to patronize 360's in any way.
I am sure that at some point a tool to convert the saves will be available. I won't hold my breath on it coming through official channels. I am sure some industrious programmer will make something. Sooner or later.