Not going to lie it would be kinda amusing if they made you “succumb to the darkness” and you couldn’t use the light subclasses again, but they would prob need far more than 1 subclass to make something like that worth it lol.

It is a “toggle”, meaning you can toggle back and forth between them. They did this to prepare for the eventuality of adding two additional darkness subclasses while keeping the UI on the character screen relatively uncluttered. If it was intended to be a permanent choice they would have firmly stated as such. If there ever comes a time when players have to effectively (and permanently) choose between light and dark subclasses, it would be well after all three dark subclasses had been introduced, provided sufficient exotic armor choices, balanced against content and (this would be very important and likely difficult) balance each trio of subclasses against [b]each other[/b]. As such I think it’s fairly unlikely to happen at all, yet if it does, it would be pretty far down the line. (΄◉◞౪◟◉｀)