Symfony3 is in fact coming; and I for one am extremely excited. We built Vennli on Symfony 2.3, and have tried to follow an upgrade path in parallel as best we can. With Symfony3 however, there are substantial improvements and changes, and the dreaded drop-off of backwards compatibility for deprecation from Symfony 2.x.
The following video does a great job of giving an overview of some of the major changes in structure, PSR, and upgradability.
Also see my other post on Symfony3 directory structure changes in more depth.