Users seem pretty satisfied with single-page apps. They are slow to load and have frustrating-to-use (inconsistent) interfaces, at least compared to my memory of 1990s desktop software. If users actually cared about performance then software would get faster over time.
Consider some company running some web application for their employees that “works best in” IE 6 or, for example, Chrome, but the 2018 version.
A third party that offers a way to run that on their iPad at the cost of a one-time 100MB download will find customers.
archive.org also might find something like it useful. How else are you going to show old sites in 20 year’s time?
Sounds like a slippery slope to me. What makes you think users will be satisfied with load times for something like that, which also probably will have a frustrating-to-use interface?