I don't see it mentioned yet, but I think it's pretty important to address that centralization goes far, far lower to the most basic Layer 1: asymmetric (ie, centralization promoting) WAN links, stickiness of IPv4, secure trust foundation, maybe DNS or other equiv, and lack of IP auth or otherwise core level mitigations for DDOS. These are core foundations, and whatever the internet standards above it's much harder when the foundations are shakier.

1. To the first, for a solid stretch of decades, WAN links in much of the world that might otherwise have supported more decentralization have been tilted towards consuming from the center vs providing anything oneself, and of course just fundamentally stagnating as well at the impetus of powerful monopolies and regulatory capture. Until a few years ago I had the exact same 5/1 ADSL link I'd gotten in I think 2000 or 98/99. It was really something at the start, and I was able to run some fun stuff of it. 5, 10, 15 years later? Not so much. The US in particular put hundreds of billions into promises of big fiber networks, which then instead got used to just consolidate and profit. Cable and big telecoms are still fighting tooth and nail to prevent efforts like municipal fiber. But once you have symmetric 100/1000 or more, an extremely reliable, sudden a lot of new possibilities open back up again. Of course in those decades a lot of effort has naturally gone into centralized efforts because what would even be the point of designing for something without much potential user base because said users were stuck on crap connections either slow period or with decent download but utter garbage upload? So the ecosystem isn't where it might be on that front either, even though it's decent for more technical users. But I don't think we should forget just the most fundamental issue that if you want to serve bits in 2023 doing so at .5/1/2 Mbps with mediocre latency is pretty limiting. Lifting that isn't sufficient but it is necessary, even if the decades of mindset and ecosystem will lag.

2. To the second, I did at least get in early enough that I could still get, for free (as it should be), a static public globally routable IP address. That has also been a major boon even back when I was stuck sipping through a narrow straw. It's hard to internet if you can't do the inter part. Workarounds to coordinate via an IP elsewhere of course exist, but it's an extra layer vs "hey I can just talk directly home (or barn or office)!" IPv6, despite its flaws, should help bring that part back as well, but the flaws and slow adoption have also delayed things.

3. To the third, how to authenticate is a perennial problem of decentralization efforts. If we at least had universal, highly reliable fully trusted secure DNS, preferably with better registrar governance as well, then that would be a somewhat practical way to bootstrap something. I could put my own domain restricted root CA public cert in DNS, and everything could then just trust all certs issued by it for that domain only at a basic level and it'd all just work. Add a few cross signing options and an ecosystem for turn key CA management appliances into the mix and it's possible to envision something pretty approachable that would at least match and slightly exceed everything Let's Encrypt offers. That's another sandy foundation that really stings.

4. Finally, if everyone has decent pipes, and was running in a decentralized manner, there is of course the potential for more and even bigger DDOS. It would be helpful if there were standards for all the various tiers of operator from core straight back to residential ISP so that attacks could be automatically reported and followed right back out the stack to whatever WANs worldwide were involved and cutting them right there, or at interconnects for ISPs who wouldn't comply. Having to layer in providers like Cloudflare, however hard and nicely they work, has papered over it but remains suboptimal. Granted, this doesn't hurt dark/gray types of decentralization, where rather then decentralizing services or communications to the world one is doing it to other trusted networks exclusively. And that's definitely still very useful.

I'm sure there's others, but at the very least continuing the fight for a really good physical layer seems pretty critical to me.