I think it’s reasonable as long as your customers know upfront that support is time bound (X years) and major releases might incur additional future cost.
This is one concern I have: SaaS is actually a really simple business model. “Pay this month, use this month”.
Introducing things like “pay one time for perpetual offline use and a year of upgrades from the date of purchase, OR pay this month use this month.” Doesn’t roll off the tongue quite as well. Maybe bad UX from a pricing perspective.
At the end of the day, as an enterprise, you have a target financial outcome: some combination of target income and profit. If a cohort of customer is willing to spend assuming a one time payment model, and you can successfully manage expectations for those customers (while minimizing the burden of doing so), it is reasonable imho. The pitfalls are customer unhappiness and the economics performing suboptimal compared to your forecasts (they become a support or engineering burden because they feel entitled to it outside of the previously agreed upon scope).
Maybe don’t offer it publicly, but test it with a a customer or two who really wants it to see what the experiment shows. Wishing you a successful experiment.
Introducing things like “pay one time for perpetual offline use and a year of upgrades from the date of purchase, OR pay this month use this month.” Doesn’t roll off the tongue quite as well. Maybe bad UX from a pricing perspective.