"Opera was first to have HTTP pipelining on by default."
How long ago was this "first"? Because Mozilla spent (arguably wasted) a bunch of time trying to get to a point where blacklisting was enough to turn on pipelining and comprehensively failed. There were reverse proxies, corporate firewalls, all sort of stuff that felt it was OK to violate the end-to-end rule when it came to HTTP or try to share sockets across threads with no locking and the experience was that both proprietary software vendors AND end sites felt that "it works in Internet Explorer, stop bothering us about this" or just outright ignored bug reports.
Over at Google they also spent a bunch of time fighting one of these protocol violatons, and eventually they gave up and switched off the speed-up for any site that doesn't speak their new non-HTTP protocol.
It's great news if today Opera has this _working_ but your reference to blacklists suggests that they just haven't done enough research/ got enough users to notice that blacklists aren't enough to actually get pipelining working reliably out on the public web. Certainly they weren't when Mozilla experimented with this.
(Some people will say this is a great failing of HTTP, but actually the same happens even down in the lower levels, there are big companies where it's strictly forbidden to use IP multicast, a core feature of the protocol for decades, because their network hardware crashes when exposed to "too much" multicast and they can't get the supplier to fix it.)