I have successfully secured a copy of Rhythm Doctor’s level editor . . . albeit from a somewhat outdated version. I don't know exactly what version it's from; the launch screen states the version as “Level Editor r27”, the character list probably contains the blue bird from Meet and Tweet, and the oneshot beats contain tentative freeze beat support . . . but I couldn't find any subdivision beat controls.

Here's where I found it, in case you aren't a subscriber to the GT-180/RW-570 broadcast channel: https://giacomopc.itch.io/rdle