As for my impressions:
Good:
The handle design is extraordinary. I've wanted a Nirvana ever since I saw a picture of one, and this lives up to that in terms of aesthetics and ergonomics. I love how they really capitalize on the stiffness advantage that's really what an integral frame helps with to make the knife as thin as possible. Even though it's a pretty big knife by my standards, it carries like a much smaller knife due to its lack of bulk. The tapered frame and lateral finger choil cutouts at the front also add to this.
The ball bearing pivot makes the action extremely smooth and keeps the centering perfect. Super fun to flick open
This is pretty random, but I love how finished the inside of the Spyderhole is. Usually you can see machining marks in them, but here is a consistent bead blast. Little details are like that are great.
In the same vein, the milled (as opposed to stamped or laser etched) blade markings work particularly nicely here.
I thought the pattern would be my least favorite part of the knife, since I like things to be regular and symmetric, but it's really quite cool in person, especially as it wraps around the knife.
The grind gets fairly thin behind the edge, and the factory secondary is very even. The plunge line is beautifully crisp. The jimping is also very effective without being annoyingly sharp.
Not-So-Good:
As many others have, I've experienced some lock stick. It's starting to get better though, so I'm hopeful.
I also find the lockbar tension to be somewhat excessive. I've lightened it somewhat by bending it out, so hopefully that gets better as well.
I'm not a huge fan of the blade finish. IMO the bead blast makes the surface a little gritty, and compromises the slicing ability and action slightly (due to friction). Also would have been nice to have some contrast with the grey frame. May try to have it polished a bit.
General Commentary:
While I agree it would have been nice to have a steel lockbar insert, I think there are a number of mitigating factors. First, I don't think it's reasonable to expect Spyderco to put out a collaboration that's better than the custom it's based on (as the custom Nirvana doesn't have one). Same goes for the non decorative pivot and the clip to some extent (Nirvana clips and pivots I've seen have been fairly boring affairs). Second, the integral construction makes it very difficult to incorporate one. While the Lionsteel SR2 and Rike 1508s have them (while being integrals), this would probably not work on the Nirvana. It would require that the insert sit on the outside of the frame, as there is no way to mill a good internal pocket on an integral. This is very different than other Spydercos with lock inserts, and requires a lot more material. Since the Nirvana's lockbar is very thin near the top due to the lateral choil (pic below), there isn't really a good place to screw the insert on without replacing half the lockbar with the insert or severely compromising its stiffness. It would also look kinda weird. </rant>
Steel washers on the frame side of the pivot would also be cool, but are similarly hard to pull off in the integral format (though I believe Reate has a design that allows for it, in their Tashi collaboration. It looks like it involves the washers going through the frame and contacting the pivot collars directly). Also, unless you plan on putting a lot of lateral load on the blade while opening and closing thousands of times a day, I don't think wear will be a substantial issue. Real ball bearings used in engineering applications need hardened steel races because they operate under heavy load in continuous use, which is very different from what a knife sees.
While trying to adjust lock tension I also noticed some discoloration on the end of the lockbar that suggests they tried to heat treat it somehow (though clearly it wasn't completely effective). Perhaps this is one of the difficulties that delayed production?
I suspect the stop pin is titanium, since it blends in nearly perfectly with the frame. I'm somewhat concerned about its hardness and wear, but like the pivot, it's likely to be a non issue.
I personally think the clip fits in with the knife pretty well, but I might swap for an after market milled clip if I can find one I like. Does anyone know if it uses the standard Spyderco three hole format? I don't have one handy to compare myself. I know RGT has a milled clip that fits that pattern.