I'll update this if I find more. For now, this seems to be a partial solution. It's a Gmail add on (except I don't use Gmail) that adds reminders. The options when setting reminders include cancelling it if someone replies, and to remind everyone in the thread. If you combine those two, it seems like — if you use Gmail's web client and have $23/month you're dying to get rid of — a decent way to add the feature. Source: over 1 year ago

As for moving your playlists, I use this app. I bought a perpetual licence for it years ago and it's so handy. I used it to move all my stuff from Spotify but I keep it installed on my phone for whenever someone sends me a Spotify playlist, I can just copy it to YouTube Music in seconds. Source: 7 months ago

Congratulations on the launch. It's great to see work in this space. At the moment, I'm using https://freeyourmusic.com/ because I have playlists on apple music, spotify and youtube. - Source: Hacker News / 11 months ago

Https://freeyourmusic.com download this app. Source: about 1 year ago

There are a bunch of services that will move your music library for you. I use Free Your Music but there might be newer/better options since I bought it. Source: about 1 year ago

There are a ton of transfer services out there, SongShift is one, FreeYourMusic is another, they aren’t perfect but will get you 90% of the way there. Source: about 1 year ago