Using Music in Vine Videos

Dear Rich: It's been a year since the Vine-Prince copyright infringement incident, and I was wondering if anything has changed or progressed regarding having music in one's vines. I ask because I'd like to expand my music criticism blogging to include seven second long real-time critiques of copyrighted song sections. How do the waters look currently, concerning this grayest of issues? Nothing seems to have changed -- at least in terms of Vine policy -- since Prince filed his DMCA notice (and we last wrote about the situation). Vine's TOS prohibits infringing content and permits Vine to remove it "without prior notice and at our sole discretion." That's all standard language for a social media site. However, we haven't seen any news about other popstars chasing down Vine videos. You can sort through DMCA notices at Chilling Effects but a cursory look doesn't reveal any Prince-style complaints. (The notices would go to Twitter, Vine's owner.) We also don't see any indication that Vine is using a Content ID system to flag material.
Is seven seconds a fair use? There are no size, shape, or time limitations that excuse an infringement, although the shorter the segment and the more transformative it is, the more likely it will be excused as a fair use. Your proposed music criticism blog (with seven second snippets) also sounds like a fair use. And if you have a strong fair use position, you can always push back against a DMCA notice. But, if threatened with a lawsuit, speak with an attorney before throwing down the gauntlet.