nomad itself will do most of this for you. If data or variables change from one deploy to the next, a nomad plan / apply would pick this up and apply the changes for you.
Doing things like this would allow you to keep the investment in Gitlab pipelines (and perhaps even help clean them up or obsolete many steps).
If you take advantage of the update stanza, you can even implement directly useful continuous deployment concepts like canary checks and blue/green deployment.
As long as the API can be reached by a nomad client on a runner in your pipeline, you can plan / apply changes in a pipeline
I would think just using Nomad is the easiest way to deliver changes, as long as you can trigger a nomad plan / apply when the conditions change, e.g. when an image for a task changes.
Curious to know if this is a useful approach. I too was attracted to Waypoint when it landed:
but for me it still feels like it’s from the future.