OK so as an update to this, I let it do its thing for a week or so and then checked the gravity, which had come down to about 1.036. At this point I "distressed" 8 pounds of frozen blackberries, threw them into a paint strainer bag and tied it closed, then racked the mead on top of them. Of course, they floated to the top, but you know what I mean. The week or so following that shuffle saw pretty much constant activity in the airlock.
It's now been about 2 weeks since then, and I've racked it back to the better bottle. Gravity reading was down to 0.96 which puts my ABV estimate at the 14% to maybe 14.5% if I account for the fermentables in the blackberries. It had turned a pretty deep red/purple color in the intervening two weeks. It looks like a merlot, and smells pretty similarly, too. Very strong berry aroma, but the flavor is not nearly as potent as I expect from looking at it and smelling it, probably because there aren't any (or at least, as many) tannins like you'd get in a red wine. It tastes semi-sweet to me, which is surprising to me considering the low gravity.
At this point I guess it's fairly stable but I plan to top it off as necessary in the coming months.