When my IPv4 died last time, I noticed it mostly because Github didn't work anymore. These days, most consumer websites just work on IPv6. That said, people whose routers were only provisioned IPv4 DNS servers did have a full outage.
If Microsoft would get off their incompetent assets already, my biggest concern would've been remembering the mDNS hostname I've assigned to my router so I could log in and see if IPv4 is back already.
The POSIX bug tracker is not accessible over IPv6, either, because their AWS setup does not support it. The website administrators refused to fix this[1].
The Valve stuff is extra infuriating because a lot of their assets seem to be hosted on CDNs that do have IPv6, but their backend servers are stick with IPv4. When IPv4 breaks, you can look and buy games, but actually playing them will fail because of DRM checks.
My ISP (TekSavvy) manages to semi regularly screw up ipv4 and what I notice is that "big" sites like Amazon, Google, Facebook, SO, etc all work as before, but it's the in-between sites, someone's blog on a search result, etc— that's the stuff that breaks.
It's easy enough to port forward v6 on some server to v4 GitHub - i'm doing it right now but can't remember the address. Think there's any demand for this, considering you can save $0.50-$2 per month per server by not having v4?
Some VPS providers already provide free IPv4 solutions.
Setting up a server works fine for server stuff, but it'd get you blocked and banned everywhere for having a data center IP while just browsing or trying to watch Netflix.
For my servers I could do it the other way around and save a dollar per month, but then I'd be sending emails from a residential IPv4 address, which will never ever make it past any spam filter.
If Microsoft would get off their incompetent assets already, my biggest concern would've been remembering the mDNS hostname I've assigned to my router so I could log in and see if IPv4 is back already.