I want to run unsigned apps on iPadOS, just like MacOS.
That said, regarding support for “slightly older” hardware. For all that Apple sucks at, they have usually been good about supporting older hardware. iPads have historically received 5 years of major releases, and then a couple years of security updates after that 5 years. The big exception being that very first iPad which was cut off after 3 years.
Moreover, software support for an old OS tends to become an issue after 2 or 3 years. Those of use who are developing iPad apps look at the traffic and start to deprecate support legacy OS versions that are in the low single digits.
Realistically, it’s about 7 to 8 years before I start to think about new hardware. That said, I still have an old ass 2013 iPad Air that I use for web browsing and messaging. Thing still works fine for that, but the third party apps are kind of stuck in 2020 / 2021 land.