It's a really interesting project. The Heart of Wales Line is not a massive area for cycling tourism - there's some MTB/bikepacking usage, and one fairly obscure National Cycle Network route (the Radnor Ring, NCN 825). So it really only makes sense in a growing-the-market type of way. But if they can pull that off then it'll make the line more viable in itself.
Coincidentally I spotted this the other day - promotion of the cycle route along the River Loire with the TER local rail service beefed up to include plenty of space for bikes.
https://www.loireavelo.fr/reservation-ter