I too am eagerly waiting for a write API, but I fear it's not going to happen any time soon. As soon as they open that can of worms, there will be far less 'authenticity' in the content, as we'll surely see heaps and blobs of spam infiltrating the streams. Though naturally, we can easily block and ignore that sort of activity.
We'll see loads of crossposting to and from Twitter and Facebook and blogs. While this can also be a good thing, it can fracture the community and conversation a bit. eg: I hate seeing Tweets on Facebook. The person isn't "there". Where do you reply? All of them? It bugs me. ;)
Having said that though, we'll end up with a great choice of Android, iOS, etc. applications to use which will most likely be far better than the options we have today.
Bring it ON!