Xenforo
used to include nested quotes natively, but they made a decision to remove that feature. On the one hand, I'm used to them. On the other hand, I can see that having only one quote level is sufficient to remind me what the conversation was about. On the other other hand, I sometimes do multi-quotes so people don't re-hash old arguments in the argumentative threads.
So, meh. I'd like to see if we can live without them and get used to it for a month or three, then find out why people still miss them - I suspect a lot of it is, "We need it because we've always had it" and not because there's a pressing need for them in our normal conversations.
For the odd situation where they are indispensable, people can create them by hand, and it's easy to do so - simply hit "reply" on all the posts you want to include, then do a little copy and pasting inside the editor to nest them. It's not hard to do - and if this situation keeps coming up for lots of people, then we can probably drop an add-in that'll make it automatic.
But let's give it some time and see what happens.