Re: Sub-classification is totally do-able. My own front-end (Hyperion) already does this, for example, here's the Leo Finance community, with only #hive-engine in the results:

In fact, if you want, you can even specify more than one tag, which will cast a wider net (Leo Finance + ( #hive-engine or #neoxian )):

As it is right now, if you want to achieve something like this without Hyperion, you need to pick a tribe's front-end and search on a different tribe's tag, e.g.: https://leofinance.io/created/neoxian

So it kinda works, but it'd be nice to make that a Hivemind feature. Complicated queries are complicated.