I’m not sure if you already know this, but you can enforce this behaviour with tag groups and category settings. The UI gives the user some hints about how the tags need to be applied, but I’m not sure how clear the UI would be for most users.
First, create tag groups for products and features. For example:
Configure your support category’s tag settings like this:
Creating a new topic in the category, users will first see this:
Clicking on the tags input opens a drop down that only allows users to select one of the products tags:
After selecting a products tag, the user is shown the list of allowable features tags:
You could also make the features tags required by adding them to the required tag group setting that’s highlighted in a previous screenshot. The order that tags are added to the category required tag group setting seems to be respected in the UI. I’m not sure if that’s intentional, but it’s helpful for this case if you want to force users to first select a products tag, then select a features tag:
So possibly Discourse already has the functionality you are looking for, but the UI could be improved.
Related to the above screenshot, users are being shown the text “Search or create” in the tags drop down, when based on the category settings, they should only be given the option to search for tags from the features tag group. The instance of Discourse that I’m testing this on isn’t quite up to date, so I can’t confirm whether or not that is a current bug. I can test that later on. In any case, if I attempt to create the topic with an additional tag, an error is returned.
This seems like a bug, but I’ll need to update my local Discourse instance to confirm that.
Edit: mentioned a couple of issues related to this here: Tag "Search or create" text is displayed when a category has restricted tags