both of which are terrible options

Which is why I am talking about a new option, which does not yet exist but I am saying that I wish that it did.

Likewise, two previous options that went from not-existing to now-existing-and-are-extremely-helpful are the ability to block an entire instance rather than each community and each user on that instance separately, and the ability to set your language preferences and have most (or at least some?) even if not all communities dedicated entirely to a different language not show up.

Likewise, if you could specifically target - either in the positive sense of subscribing to or in the negative sense of blocking - communities that match certain pre-defined keywords that communities could choose to use to identify themselves, like "hockey" or more generally "sports", or to use another example "vegetarian cooking" or more generally "cooking", then later if tens or even hundreds of additional communities were to be spun up within that same category, you could remain subscribed to or block them ALL, if you so chose, without having to make that determination for each and every single one, individually, and then repeat that process every time a new one appears. This could be modified by making a stronger choice of an individual community override the weaker choice of a mere category - e.g. if I like hockey but hate a particular team (fuck those guys in particular) or whatever.

Since these types of communities (as "sports" or "cooking" or "which app used to connect to Lemmy" etc.) rarely correlate with instance, this has nothing to do with a Local feed. Rather it is like the other two aforementioned examples in that, depending on implementation, possibly being able to affect your Subscription (adding subs to categories of communities) and All (minus categories of things you would prefer to not see) feeds. The latter is where it is most helpful b/c if you were looking for new things to subscribe to, but you will NEVER in your life ever subscribe to e.g. sports or cooking, then it saves you a great deal of time & effort from having to make those determinations on a per-post or per-community basis. Especially when they can be quite popular to other people, and thus ranked highly when sorted by Top or also Hot b/c of the interactivity with them, but when your preferences diverge from the mainstream. It helps make the whole place much more "welcoming" then, when automation more or less mindlessly takes care of such things that otherwise would require individual curation effort to achieve.

"Default behavior" can be an entirely separate matter, or it could be related but I am saying that it does not have to be. The way I am thinking of it, this would all be optional, just like blocking or subscribing to a community is now. Eventually some app could even offer a wizard to guide users through selecting those keywords that they might want, but that is getting too far ahead of ourselves here.

It doesn't work now ofc, b/c it does not exist! But it could work however we make it to work! It is only subject to the constraints of like logical possibilities plus technical implementation effectiveness. e.g., just like the language options, or applying a NSFW or spoiler tag (currently the former only applies to posts while the latter only applies to comments), when someone makes a community they could make their own selections as to which categories they want to be listed under. It could be hierarchical - e.g. "hockey" could presume "sports" but not the reverse - or not, in which case the latter would be interpreted more as a "sports, general" or "sports, other" category, rather than a super-category that includes other sub- ones.

And, just like the language options and NSFW/spoilers, people will forget to mark their communities/posts/comments, so that model could never be a perfect solution. Then again, nothing else will ever be perfect either so... it is no reason not to try? Especially if enough people and enough communities DO want it.

Anyway I am not a Lemmy developer, just saying that I hope that such a thing may come here, eventually, to make it more welcoming to newcomers, so that they don't have to spend hours and hours subscribing to this and that and also blocking others. :-)

But right now, the connection issues and defense against hostile attackers spamming the Fediverse with CP are much more major considerations, so I do not believe it will come anytime "soon".