If we assume a scenario without AGI and without a Hansonian upload economy, it seems quite likely that there are large currently unexpected obstacles for both AGI and uploading. Computing power seems to be just about sufficient right now (if we look at supercomputers), so it probably isn't the problem. So it will probably be a conceptual limitation for AGI and a scanning or conceptual limitation for uploads.
Conceptual limitation for uploads seems unlikely, because were just taking a system cutting it up into smaller pieces and and solving differential equations on a computer. Lots of small problems to solve, but no major conceptual ones. We could run into problems related to measuring quantum systems when doing the scanning (I believe Scott Aaronson wrote something about this suspicion lately). Note that this also puts a bound on the level of nano-technology we could have achieve, if we have neuron-sized scanning robots, we would be able to scan a brain and start the Hansonian scenario. Note that this does not preclude slightly larger scale manufacturing technologies, which would probably come from successive miniaturisations of 3d-printers.
Conceptual difficulties creating AGI are more or less expected by everyone around here, but in the case AGI is delayed by over a century we should get quite worried about other existential risks on our way there. Major contenders are global conflict and terrorism, especially involving nuclear, nano-technological or biological weapons. Even if nano-technology will not reach the level described in Sci-Fi, the bounds given above still allow for sufficient development to make advanced weapons be a question of blueprints and materials. Low probability huge impact risks from global warming are also worth mentioning, if only to note that there are a lot of other people working on them.
What does this tell us about analysing long-term risks like the slithy toves? Well I don't know anything about slithy toves, but let's look at the eugenics stuff discussed earlier and consider how it would influence the probability of major global conflicts, the question is not whether it would increase the risk of global conflict, but how much it would increase the risk of global conflict. On the other hand if AI-safety is already taken care of, it becomes a priority to develop AGI as soon as humanly possible. And then it would be really good if humanly possible was a sigma or so better than today. Still it wouldn't be great, since most of the risks we would be facing at this point would be quite small for each year (as it seems today we could of course get other info on our way there). It's really quite hard to say what would be the proper balance between more intelligent people and more time available at this point, we could say that if we've already had a century to solve the problem more time can't be that useful, on the other hand we could say that if we still haven't solved the problem in a century there are loads of sequential steps to get right we need all the time we can buy.
tldr: No AGI & No Uploads => most X-risk from different types of conflict => eugenics or any kind of superhumans increases X-risk due to risk of war between enhanced and old-school humans
Dr. Jubjub: Sir, I have been running some calculations and I’m worried about the way our slithy toves are heading.
Prof. Bandersnatch: Huh? Why? The toves seem fine to me. Just look at them, gyring and gimbling in the wabe over there.
Dr. Jubjub: Yes, but there is a distinct negative trend in my data. The toves are gradually losing their slithiness.
Prof. Bandersnatch: Hmm, okay. That does sound serious. How long until it becomes a problem?
Dr. Jubjub: Well, I’d argue that it’s already having negative effects but I’d say we will reach a real crisis in around 120 years.
Prof. Bandersnatch: Phew, okay, you had me worried there for a moment. But it sounds like this is actually a non-problem. We can carry on working on the important stuff – technology will bail us out here in time.
Dr. Jubjub: Sir! We already have the technology to fix the toves. The most straightforward way would be to whiffle their tulgey wood but we could also...
Prof. Bandersnatch: What?? Whiffle their tulgey wood? Do you have any idea what that would cost? And besides, people won’t stand for it – slithy toves with unwhiffled tulgey wood are a part of our way of life.
Dr. Jubjub: So, when you say technology will bail us out you mean you expect a solution that will be cheap, socially acceptable and developed soon?
Prof. Bandersnatch: Of course! Prof. Jabberwock assures me the singularity will be here around tea-time on Tuesday. That is, if we roll up our sleeves and don’t waste time with trivialities like your tove issue.
Maybe it’s just me but I feel like I run into a lot of conversations like this around here. On any problem that won’t become an absolute crisis in the next few decades, someone will take the Bandersnatch view that it will be more easily solved later (with cheaper or more socially acceptable technology) so we shouldn’t work directly on it now. The way out is forward - let’s step on the gas and get to the finish line before any annoying problems catch up with us.
For all I know, Bandersnatch is absolutely right. But my natural inclination is to take the Jubjub view. I think the chances of a basically business-as-usual future for the next 200 or 300 years are not epsilon. They may not be very high but they seem like they need to be seriously taken into account. Problems may prove harder than they look. Apparently promising technology may not become practical. Maybe we'll have the capacity for AI in 50 years - but need another 500 years to make it friendly. I'd prefer humanity to plan in such a way that things will gradually improve rather than gradually deteriorate, even in a slow-technology scenario.