I believe that developers with ideas such as mine, are usually doing work for someone else, full time.
I've written several systems, that are pretty cool, but usually are the type to be open-sourced. A recent example is a memcache like server I created, that stores the expiring data in the background on cloud storage, and can later be retrieved and reloaded into the memcache like server. Stuff like this is really great, but a lot of sites don't get to be the size where they'd need to use it, and when coming up to needing something like this, its usually created by some big company out of need (like memcache) and then open sourced. This is not something I'd go with for a start-up, and merely an example. But this is mostly the kind of programs I write.
Are there any back-end developers here that have done a start-up, and become reasonably satisfied with their success (with a back-end idea?) or should I be looking into Objective-C for a Mobile game? Creating the next remote-control my MacBookPro app, or even looking at some SAAS? In the end, my web design skills are poor, I don't want to be forced into a web niche, I want to do back-end development, but for myself, or in a start-up.