Just saw this in Yaraon's blog;
There seems to be rumour about Nisemonogatari OVA, which is supposed to be releasing next Summer according to that post. There will also be Bakemonogatari Box for movie limited addition and Railgun Movie, but no idea about any other details.
No source, so no-one knows if it is true. But it is good to know. I remember how April 1st rumour about Urobuchi doing magical girl came to realisation.