I really enjoyed the article, but I think your argument falls down in the following way:
1) Fission / fusion are the best energy sources we know of, but we can’t yet do it for all forms of matter
2) A sufficiently clever and motivated intelligence probably could do it for all forms of matter, because it looks to be thermodynamically possible
3) (Implicit premise) In between now and the creation of a galaxy-hopping superintelligence with the physical nouse to fusion / fission at least the majority of matter in its path, there will be no more efficient forms of energy discovered
4) Therefore paperclips (or at least something that looks enough like paperclips that we needn’t argue)
Premise 1 is trivialy true, premise 2 has just enough wild speculation to make it plausible but still exciting, and the conclusion is supported if premise 3 is true. But premise 3 looks pretty shakey to me—we can already extract energy from the quantum foam and can at least theoretically extract energy from matter-antimatter collision (although I don’t know if thermodynamics permits either of these methods to be more efficient than fusion). It is a bold judgement to suppose we are at the limits of our understanding of these processes, and bolder still to assume there are no further processes to discover.
Here is a rough cost-benefit analysis. I found all the numbers before doing any maths and tried to be as optimistic as possible towards your theory to account for people more intelligent than me coming up with better ways to do it if it became standardised.
The cost of freezing a cell is proxied as the cost of freezing your eggs, which is already commercially available. It is £2900 for the initial harvest and £275 for a subsequent year of freezing. This £275 is not discounted because you pay it every year. Source. Let’s assume that the clinic are nice and let you freeze as many different organ-cells as you want for the same £275 / year fee.
There are 56,000 people in the EU who are on the organ donor waiting list, suggesting there are around 56,000 people who have a sufficiently chronic failure of an organ that it didn’t kill them outright but will kill them if they don’t get a transplant. Many of these 56,000 people will get an organ through conventional means, but let’s say none of them do to account for the fact that as medicine advances we will probably be able to transfer more people off the ‘going to die’ list onto the ‘might be able to survive if given a transplant’ list. Let’s also assume that this represents 56,000 new people on the organ transplant list each year, even though the average wait on the list is around three years. Source (also I found a dodgy-looking source suggesting that 50,000 people die of organ failure each year, so the figure for the number who could benefit is probably not out by more than an order of magnitude). There are 500m people in the EU, so your chance of being on the organ transplant list in any given year is about 0.01%.
Same source as above suggests the average QALY gain for an organ transplant is 11.5 for a liver transplant, 6.8 for a heart transplant and 5.2 for a lung transplant. Let’s assume all transplants give you the full 11.5 QALYs because medicine improves.
Finally let’s assume you freeze your cells now at 25 with the expectation that they will be used in 40 years at 65. You only get one shot at doing this; you may never freeze your cells again because they degrade too much on your 26th birthday.
This means in total you pay £13900 for a 0.01% chance at 11.5 additional QALYs, for an expectated value of £10.8m / QALY. That is to say, if you would pay £10.8m for an additional year of life at the margin, this is probably worthwhile (given some very optimistic assumptions). However, this is only true if you get one shot to freeze your cells at 25. If instead you can wait until you need them and freeze them then, you’d only be paying something like £250 / QALY. You can see from these two numbers that even if cells degrade in quality to the extent that they are a thousand times harder to successfully transplant you are still better to wait until you are pretty sure you are a high-risk group for organ failure. Anyone who believes £10.8m / QALY is a good deal should also be prepared to accept a salary cut of around £115,000 / year in order to avoid a 20 mile commute since road vehicles have a fatality rate of something like 1.5 per billion miles travelled.