DNS is a centralization risk, yes. Somehow we've decided this is fine. DNSSEC isn't the only issue - your TLD's nameservers could also be offline, or censored in your country.
The only thing a blockchain is good for is achieving decentralized consensus on what value a key points to, which is what DNS is.
An alternative way of looking at this is that acquiring domains must be somewhat expensive by definition; either you enforce it at the system level, or you make it free, but then somebody will inevitably grab all the interesting ones and re-sell them to others. A blockchain is the only way to make decentralized financial infrastructure viable.
GNS is the obvious response here, in addition to the various blockchain based solutions. Nothing that enjoys widespread support or mindshare unfortunately.
Even the current centralized ICANN flavor could be substantially more resilient if it instead handed out key fingerprints and semi-permanent addresses when queried. That way it would only ever need to be used as a fallback when the previously queried information failed to resolve.
GP said it was a risk (and it is), not that there are better alternatives. Not all risks can be eliminated easily but you should still be aware of them.
BGP, but the names in question are limited to 128 bits, of which at most 48 will be looked up, and you don't get to choose which 48 bits are assigned to you.
Normally it should not have been, with cache and all, but that was the past...
Think about what would happen the day that letsencrypt is borken for whatever reason technical or like having a retarded US leader and being located in the wrong country. Taken into account the push of letsencrypt with major web browsers to restrict certificate validities for short periods like only a few days...
TL;DR: If it's not cached, does it really matter if it's offline for some time?
Long version:
If you're so popular all around that you really really want a very very short TTL, people will query all the time from all the places that "count", won't they? So it's gonna be cached.
If you're not so popular or not all around, what does it matter even if you had a very very short TTL? You're not loosing much.
Presumably if LetsEncrypt goes down and stays down for a week, the sites that go down are the ones that see that their CA went down and at no point in the week take the option to get certs from a different CA?