Hi @BenAu ,
So first thing is, this is a 'best guess' answer - we would have to ask the product team to give an official answer, but I'm fairly certain we can guess closely what it will be.
Secondly - preview services can (and most will) change before going into general availability. There are few guarantees and plenty of disclaimers when it comes to preview services.
Lastly, "using CDS" and "using the CDS connector" are two different things. While Approvals use CDS tables, the Approvals connector is not a premium connector.
Environment Variables are a Common Data Service (now Dataverse) entity accessed by using the CDS Connector which, from my experience anyway, is premium.
Unless you're building your app in a Teams Dataverse environment (which is not premium), or you use something else to store your env variables, if you're using a Common Data Service connector to access data in the Common Data Service (Dataverse), it will make your app premium.
CDS/Dataverse common environment variables are very useful if you're using CDS, Solutions and/or some level of devOps between environments, but if all you want to use are common variables centralised somewhere, there are easier and cheaper ways to do it.
Personally, I prefer to use a simple SPO list to store common variables anyway, because a list as a data source is not locked into an environment and as such, variables can be standardised across environments or localised for specific environments by adding an environment id field - all without touching CDS/Dataverse.
Hope this helps,
RT