Z. H. Darkstar
Explorer
Agree that a prestige classes isn't necessary, but it could be a fun way to give them some options and a way to embrace without the alignment change if done right.
Feels like a good use of the prestige class rules as presented in UA as the way to gain access is through an event in the campaign. And for those who don't want that path, they can still try to get cured and continue on with their regular level progression.
The reason that I'm against the prestige class idea is that your players are already in the third tier of gameplay. They may already have ideas on how they plan on playing out the rest of their careers. If this happened before they hit double digits, they might be more open to a prestige class idea. I think that the time spent on coming up with them would be better used on adjusting the power curve of your encounters.
Also, if your prestige class lycanthropes get hit with Remove Curse, how do you handle the lost levels? I think that you should hold off on the prestige class idea for another game, where you can work it in earlier into the campaign.
You got lucky in infecting the players without their awareness. I suggest letting it play out in the way the designers came up with before coming up with your own. That way you have actual gameplay experience to use as reference for your homebrew.