Hi,
as mentioned on the issue you created (thanks!), AFAIK BTtons shouldn’t be necessary anymore on 4.0.1, since mpris proxy is now built into the system.
If I’m mistaken there (just did preliminary testing as of yet), feel free to describe what isn’t working with the built-in feature that did work previously using BTtons.
Perhaps we can file a bug report here to get that fixed for everyone.
cheers!