I don't think hot patching holds the same relevance it did in 2010.
Much of today's workloads are containerized and run on roughly ephemeral nodes that can be switched out easily- K8s version upgrades force this more or less. We tent to run more and more of-the shelf hardware and worry less about individual node failures now.
In-memory updates also not magic , and can be limited as they requires data structure semantics to not really change and can create its own class of issues/bugs including security ones.
While am sure there are still use cases which dictate this type of update, the need is lot less than 15 years ago that the patent expiry will do much to the ecosystem.
That’s still a minor part of the overall Internet. Small orgs are still using traditional hosting which who knows how often are updated. I’ve seen clients sites running on managed servers that are a few major versions behind.
The small orgs using traditional hosting are not the workloads which would consider in-memory update paths ?
Typically when shops like this do scheduled updates they will happily announce downtime, it just not business critical to have zero planned downtime and also lack the skill / budget to evaluate if a given patch can be applied in-memory or not.
The overlap between those using simper setups you say and those who need in-memory updates doesn't exist?
