I really like easy access to the lyrics. If one track has it and another version of the same track does not, do I have the ability to link the two so both will display the lyrics? Conversely, if a track doesn’t have any lyrics associated with it, can I link the track to an external source to access the lyrics (purely on a select case by case basis)?
A lot of this has to do with what Roon recognises as the same track. It does a valiant job of matching and grouping compositions, but it’s far from perfect There are also some forms of lyrics with timing information that’s not guaranteed to synchronise across versions, e.g. live or extended mixes. I do agree that there’s room for improvement.
There is a Mac app called Yate which is basically a tagger. But it has the ability to retrieve lyrics via API and add it to the file in the form of a LYRICS tag. Note that these are only static, as opposed to synchronized, lyrics.
The lyrics (and all other tag data) can be viewed on one of Yate’s tag panels. These panels can be configured to display whatever tags interest you. Here is an example of my FLAC file tags for Train Leaves Here Tomorrow by the Eagles: