... is when you get them removed entirely!
I just got my TRB6PII back from a guy in Miami to have a defret done on my 6PII. The frets were kinda worn and rather than have them replaced, I figured Yamaha's flagship bass would be a good start for a fretless. It came out beautifully:
It's an ebony board with maple veneers in the fret slots.
The action: So Low. The relief: Non-existent.
I'm on HG Thor's waitlist for an epoxy job as well -- 3.5 more years!
I'm in the minority in thinking that fret lines on a fretless are rad. That looks great, man.