The main reason that I don't think that the unknown poster is Nadja Daviar is "tone."
The poster says, "shit rolls down hill," "Mmmm. Mmmm Good," and "[Hestaby] is a media whore," which doesn't "sound" like Daviar...but then again having been the voice of D who can say if she was ever even allowed to voice her own thoughts during that time. But the "Computers are optical now, right?" quote just doesn't jive for me as something Daviar would say, even sarcastically. Harlequin on the other hand...all of it fits his style.
The other thing that stops me from thinking that it's Daviar is the anti-dragon rant, "In the end, all great dragons are cold-blooded. It’s their nature. Assuming or believing anything else is just believing in a lie." But I realize that's just my inner fanboy for Dunkie talking. Still, I wouldn't expect Daviar to have that point of view (especially if she ever was aware of the Big D death's as him sacrificing himself for the protection of metahumanity). It comes across as contrary to a scene out of
The Prestige in SL,
"Dunkelzahn is dead," Nadja said with a voice hardened in a way Rory understood perfectly. He stopped smiling, "I seem to be the only person to truly understand that our actions are his legacy. It is not what we think he wanted that matters, but what we do with what he left us."
Of course it could always be a case of misdirection; using tone, style, etc. that isn't consistent with the known style of the individual making the posts...but making that assumption makes the mystery nearly impossible to solve...unless the falsified style is in the style of some other known individual, such as Dawkins Group posting as if they were Harlequin (an example only).
The one thing that I'm unsure of is whether Daviar has ever been confirmed to be an immortal. I don't think she has and thought there was some reference to someone finding out she spent time in an European orphanage in her youth (not that that couldn't have been falsified of course). But after a quick search I couldn't find the book so I may just be getting things mixed up. Does anyone know if there's a canon source indicated/alluding to Daviar being an immortal (or not being one)?
On the other hand, Daviar would have interests in nearly every post, from Azzies to dragons...but it just seems more in the style of Harlequin. Even the "Art exists for its own end," media-piracy sounds Harlequinesq.