As for knowing the same songs, I made friends through genre-related social groups - the goth/industrial nightclubs, and the Eurovision fanclubs / events. It's nice that generally everyone knows the same Max Martin songs, but there's deeper friendships to be had at clubs where everyone knows your obscure niche - whether it's arguing that Euphoria is still better than Heroes, even if Mans & Petra are the best hosts. Or if it's goths bitching over the shared experience of falling down the stairs trying to get onto the goth club dancefloor before Dero from Oomph yells "Gott Ist Ein Popstar" or "Augen Auf, ich komme"....
E.D. Hirsch, Jr. wrote "Cultural Literacy" in 1987, with an update in 2002 as "The New Dictionary of Cultural Literacy". It's a huge collection of thousands of words/phrases/concepts/devices/people/places/etc, across multiple categories, that most Americans will already know the majority of their meanings, or at least find them somewhat familiar. I personally like randomly looking at the proverbs and idioms and sometimes finding parallels in other languages. It'd be interesting to go through it at random with a 7th grader and see what they've picked up -- like who says "there's more than one way to skin a cat" these days, but also who grew up in the US and doesn't understand its meaning? The book contends that about 80% of the knowledge shared by the literate has not changed for over a hundred years. Meanwhile for the 20% that changes (or is brand new) Asimov once wrote a chapter (9 in http://www.arvindguptatoys.com/arvindgupta/asimov-on-numbers...) on how so much once-common knowledge has been happily forgotten -- who needs to know about compound addition?
For the professional context, https://apps.dtic.mil/dtic/tr/fulltext/u2/a219064.pdf et al. claim you need to know 70k plus or minus 20k things in your field to be an effective expert. I think it's also why it can be easily rewarding to chat about work with colleagues, you both have a lot in common just on the basis of the shared profession.
In short, I wouldn't worry about running out of shared knowledge, nor even shared preferences and tastes, for yourself or for the world.
So I wouldn't say I've explicitly made many if any friends over shared interests in music, but then once I had friends for whatever other reasons, we shared a lot of music with each other. Hardly any of them weren't "in" to music, and indeed some of them quite the opposite; they ended up in a band together (and I would occasionally incompetently noodle along with them on vocals/bass/guitar, but I wasn't remotely good enough to play out like they were).
In practice, though, I'm sure there's quite a bit of sharing musical tastes between friend and interest groups; it wouldn't be literally everyone listening to different things.
I would wonder does increasing consumer choice ultimately erode generational identity a bit, though. So much of the "what is a boomer/gen X/millenial" is founded in what popular culture everyone was consuming in a given decade.