I personally wouldn't convert your players unless you are starting a new campaign with new PCs. I think forcing the change there might be a bit much.
However, I think anything around that is fair game. Bringing in the journey rules, sure. Maybe offering a combat manuever as a special reward (or a special ability of a particular vanguard), yep. A rare spell as a special gift, oh yeah. etc
Aka feel free to add in the LU rules around your players, but I personally wouldn't force a shakeup of the PC races/classes/etc for longstanding characters.
However, I think anything around that is fair game. Bringing in the journey rules, sure. Maybe offering a combat manuever as a special reward (or a special ability of a particular vanguard), yep. A rare spell as a special gift, oh yeah. etc
Aka feel free to add in the LU rules around your players, but I personally wouldn't force a shakeup of the PC races/classes/etc for longstanding characters.