Yes, I've worked on transactional systems and APIs for many years so I do understand your use cases here.
However, on the web, many APIs are not reliable or transactional, and are more "best effort", so quite often you are going to have to check for success of your action. The public Twitter API does not offer any guarantees that actions will be successful, although our API return codes would usually be a reliable signal.
In this case, as we explained in the original post, it is too complex for us to offer a reliable solution here given the newer mobile contexts etc that the web intents have to operate in. There's no plan to introduce a callback on completion.
The best way for you to see whether the action was successful is to read the user's timeline in code and see whether the Tweet was posted.