my main thing when we're talking that long is the number of applications goes down due to costs going down and further breakthroughs happening.
kind ofLarger batteries in the future could cost a lot less, a new tech breakthrough in batteries/panels or both could outperform today's tech of any kind by a lot, or other unforeseen stuff. The longer the timeframe the more likely vastly better stuff will be cheaper than today's stuff (not a guarantee but tends to happen especially in tech). Saving half of your money today and spending it at 20 years instead of 50 isn't necessarily a loss depends on what you can get in 20 years for those dollars.
I will 100% agree application matters enormously .. use the right tool for the job .. pros and cons for a the needs of a specific application .. devil in the details.
but .. as for the other part ..
The rate of technological improvement has been slowing down for many years now .. there is not infinite growth .. sure progress is still being made .. but it's slower and slower each new decade .. less and less improvement each new decade.
The easiest place to see this is in computers .. which used to be the poster child for exponential technological improvement .. from 1995 to 2000 a home PC got about 20x better in almost every way faster , more storage , more diversity of applications , etc .. but from 2000 to today 2020 .. no where near that .. sure they have continued to get better .. but how much it is further improved is less and less .. the rate of progress is slowing and slowing .. today's home PC is all of about ~4x better than the PC from 2000 .. which is good .. but 4x in 20 years is vastly slower rate of improvement than 20x in 5 years .. at the current curve of decreasing rate of improvement , computers can be reasonably expected to get maybe 2x better than today , over the next ~30 years or so.
But that same over all trend of .. slowing of improvement .. is seen in pretty much all technological sectors .. cell phones , batteries , material science , medical care , etc .. etc .. not all sectors are slowing at the same rate .. but the rate of improvement is slowing in all of them.