Exclude activity types from budgets

We use budgets to track order cover, so often need to exclude some time - e.g. pre-sales activity, or certain product owner time.

Ideally, we group work for an initiative into epics and then add that epic to the budget...but issue is that if this non-billable time is booked against the epic (or below), it's included in the budget.

We could add all features under the epic to the budget, but what if billable time is at epic level? Or we forget to add a new feature? Excluding individual time tracks would be v labour intensive.

This suggestion is very similar (but bases off the user):

https://support.7pace.com/hc/en-us/community/posts/115018127083-Budgets-Allow-Including-Excluding-by-User

Would it be better to have budgets respect the billable flag (seems weird they don't already...), then default that certain people and/or activity types are billable/non-billable?

If you didn't want to have budgets respect the billable flag for backwards compatibility, could you add another total to the budget (e.g. "Tracked (billable)")?

I'll stop solutionising now...