Is it plausible that Apple might release a 12" iPad Pro this year? Sure it is. Will it, as some media outlets are reporting, be "targeted at the enterprise"? Of course not. When has Apple targeted the enterprise with anything substantial since Jobs's return?
To quote John Siracusa, "enterprise means that the product is purchased by someone who is not the user." Apple has spent the last sixteen years targeting the end user with every product in its portfolio.
But so many narrowly-focused journalists conflate "pro" with "enterprise." Really, though, they couldn't be more different. "Pro", in the context of Apple, refers to the creative power user, to the individual recording and mixing albums, editing films, or building great software. "Enterprise," generally speaking, refers to cheap commodity computers buttressed by expensive (but usually mediocre) software and services. The Dells and HPs sold in bulk to Fortune 500 companies are worlds apart from anything Apple offers under its "Pro" branding. There's simply no comparison.
A 12" iPad Pro might make sense. But it won't be targeted at enterprises. It will be targeted at artists, makers, and creators, at the free-thinking individuals looking to get the most out of their devices. You know, like every other product Apple makes.