This evening I took a break from the code I was writing and put together an addon: https://github.com/emanuele45/TwitterPoster
The idea is the simple one to post to Twitter when a new topic is created in a list of selected boards (among those visible to guests... well, actually is not really that much enforced, though that's the idea. :P).
It should work, not tested much because Twitter wants my phone number to create an application and since [put usual stuff I don't want to give my phone number to Twitter/Google/etc.], I just quickly used an existing app for the
ElkArteForum (https://twitter.com/ElkArteForum) account to verify it was posting right.
If anyone is interested in testing it and/or adopt the addon feel free to go on and let me know! :D
ETA: additionally I just realized I tested it on Elk 1.1 code... it shouldn't change anything in regards to this addons, but worth mention. O:-)