The problem I think you are trying to solve isn't much of a problem.

I've been developing with CMS applications for 12+ years and have never once ran into any of the issues you described above (failed upgrades, hackings, site-jackings, buggy plugins) to such a degree that I wanted/needed to completely switch the CMS platform.

I'd urge you to NOT build a product for developers. I know it's tempting because the ideas we (developers) come up with follow the 'scratch your itch' advice. I wrote a blog post about this: http://www.travisdoes.com/you-itch-sucks-scratch-somebody-el...

I'd highly recommend you focus your efforts on building a B2B SaaS product. There are millions of great opportunities to build boring, but profitable niche products.

If you need help finding some ideas, shoot me an email.