Hi cyberience and welcome to Tiki Community!
You can use the field category on a tracker, and it will shown its child categories as checkboxes.
In addition, you can tell your users to monitor categories for changes. This way, when someone select that option in the checkbox options in the tracker form (category), they will get notified by email.
The emails sent from trackers are not easily modifiable so far (I'm after this, looking for a coder to allow it).
Yes, I fully agree. It's not done yet.
I've been suggested to have a look at JQuery API (see PluginJQ ), but didn't go anywhere yet.
Hope this helps, and please, report back if you manage to succeed in the Jquery world!
Cheers, and welcome again