Is it still possible to double / triple book?
No and yes. No, I don't think you can book ADRs with closely overlapping times (maybe less than an hour?). But you can book more than most reasonable people will eat. For example (and I know I'm risking getting flamed here, but am hoping folks will not be judgmental), I have ADRs at H&V at 5:40 and HBD at 7:35 on the same day, about 6 weeks from now. I originally had MM at 6:55, but wanted to move closer to the front of the park and earlier in the evening. When checking yesterday, the H&V and HBD both became available. The H&V ADR meets both my criteria, but is an over-priced character buffet with questionable food. I prefer HBD for food, but it's getting close to potentially overlapping with SW fireworks time of 9:15. Unable to make a decision quickly, I was able to book both, and also cancelled the MM (which someone else booked within a couple hours). I will decide within a day or two which I want, and cancel the other.
Am I holding an ADR I won't use? Yes. Will I release it well before that day? Also yes. Honestly, I've done this with more than 2 dozen ADRs while planning this trip. (I know, I need to get a life.) We're taking the DGKs for the first time, and I want everything to be as perfect as possible!
I have read posts, and am sure they are accurate, that there are people who in a situation like I've described would hold both until the day before. I don't think that's right, and would not do it myself. I could get upset about other folks doing it, but rather than get all worked up about something I can't control, I choose to look at it as an opportunity to pick up day-before reservations, if I would like to do that.