There are some discussions/threads here about ways you might save out your work if you were afraid Adobe software would not read the edit list on your RAW. Others reading this please chime in if you believe this is not going to be possible, though, after making the jump to the subscription model.
Possible to save it, sure. Possible to do anything with it, probably not. Whether your settings data is stored in a separate XMP file or in the Lightroom catalog, you aren't likely to be able to take the data from version n
of LR and load it into any version of Lightroom older than n
The problem with this plan is that it basically locks you into paying $9.99 for the rest of your life. Don't think of it as paying $120 per year for LR and Photoshop. Think of it as paying a $7,200 lifetime membership fee $10 at a time. That starts to look a bit less attractive.
Now as long as LR is still available for purchase, that's not a big deal, because you can always pay $76 to upgrade your last purchased version to the current one, and then jump off the treadmill. Unfortunately, given that Adobe also said that the purchased versions of Photoshop would continue to be available right up until the day they changed their minds, I don't trust Adobe to keep Lightroom available for purchase unless the overwhelming majority of their user base says, "Oh, hell, no" to the subscription model. And that's where the real danger with software rental lies. It's a Faustian bargain.
And, of course, unless you use Photoshop regularly, given that this is still almost double Lightroom's roughly annual upgrade cost, you're getting ripped off even at $120 per year.