"It's 10-100x more difficult to design the production system than the engine itself"
So what we really need is to invest and innovate in the production of complex telescopes/probes/etc such that it doesn't cost $10 Billion and 20 years to build, and the loss of one wouldn't hinder the overall production.
What we really need is to standardize as much of the telescope as possible.
Communications? Don't need to be bespoke per satellite. Guidance/Navigation? Doesn't need to be bespoke.
Ultimately only the actual optical payload really needs to be bespoke. Commonality of components and design can drive down prices and reduce time-to-launch.
people who don't care about pointing accuracy end up spending zillions of dollars so they can have fraction of an arc-second precision
satellites that are in Earth orbit have different thermal needs than one in L2
satellites that are less weight sensitive waste money on carbon fiber
an instrument that needs to be cooled down to 50K doesn't need a JWST-tier cryocooler, etc.
You could try having a range of things, e.g. small, medium, and large bus with a handful of interchangeable subsystems. But you're still asking designers to sacrifice their precious size, weight & power requirements
1. Forensics difficulty. You need extensive data to debug issues for complex systems. You can collect so much more data from terrestrial testing, which allows you to do the extensive forensic analysis required to achieve the required component reliability. Once you put a telescope in space, you can't inspect it anymore. A lot of the sensitive components which might fail on JWST have to be inspected to microscopic precision in order to perform adequate failure analysis.
2. Design requirements are far, far more precise. Many failures in deep space are effectively impossible to correct in later iterations due to point 1. Telemetry and sensor data is enough to debug rockets, but for JWST you would need to ship so much extra data/sensor infrastructure alongside the telescope that the whole project becomes recursively intractable.
The system complexity is so high that you absolutely must have the ability to make arbitrary system corrections because the chance of "building everything correctly the first time" is effectively zero, even with perfect hindsight! Essentially, any time you build the thing from scratch, you will always find mission-ending statistical deviations. The objective of on-ground testing is to identify and correct those specific deviations, until the whole system is within design tolerances. If you were to totally rebuild it, the next iteration will have a totally different set of statistical deviations which will need to be corrected. This process of development involves "hardening" the entire system through extensive testing, because it impossible to build a fully-hardened system to start with, even after "learning" from previous attempts.
Kind of like in computing, where we moved from a single ultra reliable mainframe to tens of commodity hardware.
Commercial software development practices might be relevant where you can fix things overnight, but this is hard science instrumentation made of atoms, you ship things that must work as expected because the whole point of all this is making better measurements as the field evolves and there's a scientific case for doing it. It is not about selling production versions of the experiment to potential customers.
Instead of sending up 1 super precise super accurate super reliable telescope let's send up 1000 mostly POS telescopes and combine the results using AI of the 900 which actually make it to orbit and return useful images.
I'm hardly saying that's a 100% working plan, but, I think that kind of paradigm shift which is required.
It's not like space telescopes need any of the valuable orbit space, and even if they did it's easy to put thrusters on board that can de-orbit them or move them to a graveyard orbit (depending on their operational orbit) in the case of failure.
To summarize, you have to have the ability to correct statistical aberrations after manufacture via extensive validation and testing, as opposed to design aberrations which can largely be eliminated through destructive iteration. Without the former process, you'll launch a million telescopes and not a single one will work.
Remember that Hubble was essentially useless until heroically repaired the first time by Story Musgrave. Many subsequent repairs were required to get the best pictures from it - like the deep field, long duration picture.
If each of these had a high-grade commercial camera lens pointed towards earth, you could have real-time viewing of the entire planet with just a little bit of math. With a bit more fun (and for each click of optics improvements), you could "Bullet Time" view a great number of things...
If each of these had a high-grade commercial lens pointing outwards, what could that be used to capture? At scale, it seems like doing diff's against all the images would reveal a huge number of previously unidentified asteroids and other near-earth objects.
What if you put "very good" optics on them? Or a radio antenna pointed out? Could you make earth sized optical or radio telescopes? Seems like you could.
It's increasingly looking like the assumption each one needs to drive the state of the art, and each one needs to be "space grade at 100x the cost" is a fallacy simply because launching was historically so expensive.
[1]: https://en.wikipedia.org/wiki/Very-long-baseline_interferome...
With asteroids, you don't need to diff telescopes at different locations; you can just diff the image taken at one location, 15 minutes apart.