The thing with Twitter is, that they don't really want to kill their app ecosystem, but really just want to keep growing because of their app ecosystem, they only want to be the transport layer so it is highly unlikely that they would come out and kill your project by duplicating it.
A perfect example is the completely under-powered lists feature, the API is super powerful but twitter's implementation is as barebones as it can be, possibly because they want to encourage other people to build on top of their stack.
Have you looked at the Streaming API for your ideas? You can also get full firehose access if it really does become successful. Obviously, sharecropping on someone else's farm is never a brilliant idea but if you're going to do it, Twitter may not be such a bad place to do it...
