So like, a view of all changes made between previous version to this version?

I know there's a workflow approval workflow (awkward sentence haha) that can be run to review things before they're published, but, I haven't seen a comparison tool yet.

I will be watching this thread...

Comparison tool is what I had in mind, yes. Something snappy, like a PowerShell script that downloads latest published workflow "Abc" from Site X on List Y and compares it with an NWF file on disk to confirm that it's either the same or different and then (would be nice) exports the blocks of XML which are not the same.

A view of all the deltas from start to current would be quite useful.

Can you expand a little on this?

Workflow version numbers would surely cover this off for you?

If you need a little further detail the DB's will have that for you, you could probably create a view of some kind.

Absolutely. So imagine I have a workflow with a Flexi Task action that has a custom task form made with Nintex Forms and inside that custom task form is some custom JavaScript. I implement a change to one line of JavaScript in that task form. I save to my development environment, export to NWF, and check in to TFS Online for my colleague to deploy to production. My colleague goes ahead and deploys the workflow. I want to confirm that the workflow my colleague deployed is the same workflow I checked in to TFS Online. I'd like to be able to do this without having to do this manually (e.g. export from production by hand and use WinMerge).

Do you want to check just the version, or the code itself?

The code. The version doesn't tell you what was published, only that something was.