Existing Symbian s60 applications will not run on Symbian^2 !

Symbian Foundation doesn't plan OS upgrade.
They don't plan neither some applications compatibility on the platform, because there are, besides the "public API", some secret APIs: "Platform API" and "internal API" and the secret platform API CAN CHANGE between the releases!!!

For developers this means: mysey, mysery...

From the comments in the blog you linked above:
http://blog.symbian.org/2009/03/12/i...-release-plan/

Quoting David Wood:
> (The Symbian Platform makes a commitment to preserve
> public APIs in between releases. However, we reserve
> the right to change platform APIs.)

> A device like the N95-3 has a large amount of additional
> software in it. Some of that extra software may well
> use platform APIs, as well as public APIs.
> When the operating system moves to another version,
> the platform APIs can change (although the public
> ones remain fixed).

@David: the platform API is basically a private API, right ?

David Wood:
There will be material about the different API categories on the forthcoming new version of http://www.symbian.org. Here’s a quick explanation in the meantime: “public” APIs are expected to be maintained between releases; “platform APIs” are available for people creating software to be built into devices or to be included in the platform itself; “internal APIs” are for use only inside a single package.