Over the last 2 upgrade cycles (2012-2014 and 2014-2016), I've developed checklists that I follow. They're more fleshed out than your list, and much more tailored to my environments.

However, each upgrade has been different too. E.g. in 2014, the cardinality estimator changed, so I paid more attention to particular queries & jobs that might be affected. In 2016, SSRS & SSAS tabular changed quite substantially, plus Cozyroc changed a ton, so a lot more time was spent upgrading & configuring those components than before. So I simultaneously feel that (a) my checklist wouldn't be comprehensive for the next upgrade, and (b) there are things on my checklist that might be overkill and I could safely remove them now I'm already on SQL 2016.

I would love to see better checklists, along with reasons why a particular thing should be checked. For example, a lot of people suggest updating all statistics after an upgrade. I can see the logic in this. But, updating all statistics can take 5+ hours. Should I really do that as part of the upgrade? Is it safe to bring systems back online, then do this the next night? It's easy to recommend "update all statistics" but more contextual information would help when faced with the practicalities of fitting that into an upgrade window.

I'm in two minds about in-place vs. side-by-side upgrades too. Side-by-side does allow for a new O/S, new hardware, etc. But, it also increases the risk. Suddenly I have to migrate a ton of things that I wouldn't otherwise have to worry about (operators, alerts, linked servers, agent jobs, SSIS packages, file/folder permission quirks, firewall settings, SMTP permissions, master keys, certificates, application connection strings, etc.) Obviously it's good to know about all these little things (in case of a real disaster), but it does add a lot of overhead to an upgrade (and a risk that something goes wrong not because of the new version, but because of the new server).

Another upgrade question I've had recently is regarding cumulative updates. There's no clear checklist for those. A full version side-by-side upgrade seems overkill for a cumulative update. Even, for example, the SSISDB catalog. Do I need to update the catalog for every cumulative update? Or is it ok that SSISDB catalog is on SP1 CU0, yet I've applied CU2. I haven't been able to find a clear answer.

I'll just end by saying that upgrades are not the most favourite part of my job. 😀