Why have they been delaying Kizumonogatari for so long?
There's no doubt to the popularity of the Monogatari series that fans are clamoring for Kizu, but since it was delayed by production AND the immense popularity of Madoka Magika, what's probably happening now is that Kizumonogatari is likely being planned to be released towards the end of the franchises finale, as a reflective issue. 

No source for info, just an observation and estimation. Tsukimonogatari marks the beginning of the end of the series, the final arc so it should be within this year that we hear news about it.