Why? A lot of people have been asking for this over the years. It hasn't happened because of DW's lack of workable API: the current API was inherited from LJ, and hasn't been updated to handle DW-specific features.
I have experience here. When I first wrote Joule, LJ's API didn't support the search it needed. So it worked by scraping-- that is, requesting the pages as if it was a browser, and parsing the HTML directly. Dwim should work the same way. It's especially easy with DW, because you can request pages without any styling in the way.
How? I've got a lot of ideas, but I'm carefully not diving in to coding it before we've talked about it here :) In particular we should discuss:
- the UI
- how the back end will work
- whether and how we deal with posting while offline
- what we're going to do about including images (especially for "share to DW")
- what toolkits would be appropriate
- whether anyone wants to help with coding or design or documentation
- a roadmap of what features should appear in each iteration
I'll post more in the next couple of days as I write up my notes. Feel free to post and discuss too.