I really can't see them converting Lightroom to a subscription only service. There simply isn't enough to it to warrant such a move. It is already a super cheap bit of software, and has next to no barrier to entry. I expect that they will continue to offer Photoshop+Lightroom bundle for $10 a month, but I doubt it is very likely to be dropped as a standalone package sold as a retail box anytime soon. (They might drop physical packaging, and go with just direct download, but that is no different from the copy of LR4 I already own.)
I would be very surprised to see them go back on the earlier announcement that LR is remaining with the option to buy it outright rather than having to go with a subscription package. At least for a few more versions. If they don't then they're just undermining their reliability, and I really can't see their PR people wanting to take that kind of a risk. They've gotten enough backlash and mud thrown at them over their cloud transition as it is.
Canon EOS 7D | EF 28 f/1.8 | EF 85 f/1.8 | EF 70-200 f/4L | EF-S 17-55 | Sigma 150-500
Flickr: Real-Luckless