Symbian releases microkernel

Am I right in thinking that if one wanted to load this onto a symbian based phone, having patched it, there would be no chance, because the patched version would no longer be signed by the device manufacturer?

If not, why would I want to waste any effort writing code for a platform where the manufacturers have this inequitable hold over their devices? Especially when they can grab my source, trivially patch it, sign it, and sell my own code back to me, which would be somewhat irksome.

If on the other hand, it is possible, what's to stop me stripping out stuff I don't feel the need for (including stuff like DRM enforcement and tethering prevention)