There are some valid points being made here and there in this thread that are not being fully connected by many of us readers.

Why no Bryce SDK?
Firstly, as simplistic as everyone says Bryce is, it has some special talents that no other application has. Someone already mentioned about Artmatic and Eric Wenger. What is not being connected by readers of the thread so far is that the procedural generators in Bryce's Material Lab and Terrain Lab are protected by copyright laws and are being used in Artmatic as well as some other applications. Even though Daz owns the Bryce software, they do not have the legal right to mess with certain areas such as procedurals, mapping modes, and some of the other Bryce specific abilities we are all so accustomed to using. Ever wondered why there is no World Cubic mappimg in some high end applications, no Object cubic or sinusoidal, its because these guys still own the rights. Most other applications use UV mapping so all these seemingly essential modes in Bryce are useless in most other applications.

So yeah, Daz owns Bryce....just not every line of code within it. Or a better way to state it, Daz is allowed to distribute Bryce, but not to give away its individual parts because some of those parts are still intellectual property protected by the original creators.

Artmatic and Mojoworld are at least two popular applications I can think of that were developed in some way by either Kai Krausse, Ken Muskgrave, or Eric Wenger after the days of Bryce and are part of the reason why a Bryce sdk still cannot be released. This is also the reason Bryce cannot be made Open Source like Blender.

Two of the most popular ideas offered by the userbase both shot to hell...

It isn't that Daz is stupid, it is literally that their hands are tied legally. 

Sad situation, no?

What about a Bryce 8 developed by Daz 3d then?  Here's why it so far it hasn't happened:

No one has managed to convince Daz3d that Bryce can do useful things that other applications cannot. Show me a look you can achieve in Bryce that cannot be achieved in Vue, Terragen, Carrara or Blender and then maybe we'll be onto something. While Bryce competes just fine in hobbyist markets it has no footing at all with professionals, and professionals are the ones who are dedicated purchasers of software to fund development. Poor people like myself who got into Bryce for it's low cost are not the people who keep the world spinning, you need the big spenders for that, at least for a lot of it. You can see the same thing happening with Carrara development. it too has officially stalled, but I still think we will see a Carrara 9 or 10 before we will see a Bryce 8 or 9.

Bryce has not grown with its user base, it became a tool for introductions to cg only as a stepping stone to other applications. I think lots of 3d software owe their large userbases to Bryce because it was Bryce that got them into cg in the first place. But once they "outgrew" (you can never outgrow Bryce) the obvious tools in Bryce they moved on to other applications which can do things more easily by being 64 bit, faster rendering, better instancing tools, better lighting tools etc.

What next to develop with Bryce?
For example, the rendering engine. While there are lots of improvements that could be made to the engine why would anyone bother? In this modern day of unbiased lightening fast rendering who cares about a new engine if it remains biased and slow as heck? The only other render engine I'd like to see added to Bryce is an unbiased one for Bryce, anything else is still going to leave Bryce behind its competitors. Not that the only engine should be the unbiased one, I actually think we should have two, the current and a new unbiased one. Either that, or they need to develop a plug-in or bridge that gets models into unbiased Octane or Lux, though I strongly prefer Octane. But spending time on this current biased and glacially slow engine is a huge waste of time considering the rendering climate today.

Bryce needs to be made 64 bit first and foremost, but that requires a ground up rewrite, and for that amount of diligence one could develop an entirely new application for which they did indeed own every single line of code...a lot like they did with Daz Studio.