Odoo has already started to communicate about version 15 changes. 

1) via the publishing of the code (technical skills needed)

You can see the code of version 15 at:

https://github.com/odoo/odoo/tree/master

The term "master" in this context is "the next version".

You can see for example for each commit we publish the intention of the change and link it to any Odoo ticket or internal task:

https://github.com/odoo/odoo/commit/c8f029744bcb2d438ec544988c56c5151696ea93


2) via runbot running instances (functional skills needed)

You can see a working instance, updated several times a day at:

https://runbot.odoo.com/

Click the blue "arrow in the window icon" within a green  #enterprise section on the MASTER branch.

3) via intermediate release notes

You can watch for release notes of Odoo 14 point releases on our website (we release portions of v15 prior to October each year, generally every 2-3 months). Generally, they match this pattern:

https://www.odoo.com/odoo-13-2-release-notes

https://www.odoo.com/odoo-13-4-release-notes

Note: the Enterprise Edition of Odoo is published via a private repository.  If you don't have access, you use methods (2) and (3) to keep abreast of changes.