Welcome, @Jayme_Simpson,
Until/if this request is implemented, perhaps consider these workarounds if you haven’t already.
If you homed (added to a project) those subtasks, then you could use that project to easily provide the filters and views you need. This could be automated, potentially, with rules or templates, depending on your workflow.
A related approach would be to home those subtasks to the very same project their parents are in, offering the same benefits, but with a a side effect. That’s all explained in another answer I gave to a related question:
Finally, advanced search saved (starred) reports may offer limited relief too, since you can specify “subtask” as a criterion in the search (though be aware it means any level of subtask, not just the first level).
Thanks,
Larry