I also have 3x64GB microSD cards that I swap. It's a bit of a hit time and battery wise, but often you can plan ahead. It's true that you don't NEED to do a library scan, but I usually do it for convenience.
My other solution is using an inexpensive SD>microSD adapter (~ $6 from China!) with a 128GB SD card. It works, but I wouldn't recommend it on the go. It's very easy to disconnect it, but it works fine at my desk at work. Unfortunately my HD music library is getting too big for all of these options. And 256GB SD cards are still very expensive.
I may try to find or fashion some kind of case that would hold it more securely.
I believe that 128GB microSD's are still a ways away.