I've been patiently stashing away one of every drive-able book I get for... I think since the last Reading Drive. Do I still need to hang onto them?
no, this has been asked many times and the answer is always the same: there will never be another reading drive.
It's pretty safe to sell or read them, as you see fit. :)
I think more people are happier to not stash books of each kind every year, and just read or sell them instead ;) I won't be surprised if that's a factor of its retirement.
Oh... thanks for asking. I'd started hoarding books too because I wasn't a member during the previous reading drives.
- During a reading drive, you could donate books for points that could be used in a prize shop after the event ended. It was sort of like the item drives we've had the past few years, except you could only donate one copy of each book.

You could hoard books, and I think the reading drive would let you turn in one copy of every book (at least one of them was one copy only, not sure about others that I wasn't around for) to earn points. At the end, there would be prizes you could spend the points on; those are now in the Antique Shop. There were also achievements for turning in books.
Staff have said that there won't be another reading drive like the way it was done in the past, but there may still be other item drives with various items. Like what they did with the snowman contest a couple years ago, and Babette's babies. You can turn in items from certain restocking shops, but the shops aren't announced ahead of time so you can't necessarily hoard things on purpose to use for an item drive unless you wanted to hoard everything just in case.
But even those kinds of item drives don't seem to be very common anymore.
Thanks for the detailed explanations! I only vaguely remember it, but it was so long ago that I couldn't remember exactly what it was about. Does sound a bit frustrating tbh. Especially when you're like me and have shifts during the busiest times of Subeta x_x