Hi there @cocoapa! Welcome to the community!
Foundry will continue work as it does today. Foundry v2 will provide many longtime user requests, new stacks, and the integration of lots of new features. I’m not changing how Foundry fundamentally works. It works really well as it is and that functionality is what makes Foundry an easy-to-use, but powerful framework, IMHO.
No, you will not need to rebuild your sites to use Foundry v2. I’m not looking to create more work for users when I don’t need to. If something fundamental changed in the framework that made it necessary for me to do so I’d have announced it long ago.
This new version will simply install over top of your current version of Foundry and add all of the new stacks, features, etc.
Hope that helps.