Hi-
This comes up from time to time, and has across the past decade. Not saying it is a bad idea, but there's a lot to consider, and the institutional background on the discussions is not always present for each time it is raised. I don't want to prejudice or bias the dialog, because there MIGHT be some advantages for SOME of the use-cases out there.
The argument exists that DNS moved a static list called HOSTS.TXT to a distributed and more efficient lookup model back in the 1980's, and static list model used in the PSL or other static lists like it carry some of the architectural pros and cons of a system that 'evolved' a number of decades ago.
It seems that there may have been a number of benefits of a local file that may have been overlooked a the time which may be hard to leverage DNS for.
Where we have hit a wall in the past with something like this is where we're making assumptions about how everyone is using the list.
There is a segment of the user/integrator base and their use-cases that moving away from the static file into DNS makes sense for.
There is also a significant segment of that base where it is absolutely not going to work. An example (and not the only one) would be "omnibox" browser implementations that use a local logic to determine if DNS gets consulted at all, or the user entry gets sent instead to search. To DNS-ify the list lookups would increase DNS traffic and introduce latency. This is not a good thing, as browsers compete on how responsive they are for page loads.
That is just one example of X many, and we don't know X without an expedition.
Unfortunately, without such an expedition, many of the IETF proposals end up being solutions in search of a problem. Maybe better stated, solutions coming from the perspective of the problem set that is self-identified by the proposing expert(s) absent knowledge of a full set of X, until some time as we determine a more comprehensive universe of use-cases to solve for X.
The "X-pedition" (sorry, Marvel mutant nerd here, couldn't resist) challenge is that there is not a global list of users or use cases to allow those who might seek to come up with a standard within the IETF process to propose something that would/could suffice. Unfortunately there exists no means to poll people who implement/use PSL via libraries (or directly) into their code, and there's a thinly stretched layer of volunteers that MUST focus on the core _stuff_.
I've invested time in dialog with a number of those proposing solutions in search of problems attempting to define a large segment of the use cases, but these efforts will still fail to define "X" entirely, and we're still in a place where there would need to be a large effort into an expedition to gain more awareness of how the PSL is being used be everyone. There is not a PSL login or user list. It is fully given to the world from the volunteers and the great people at Mozilla who help cover the CDN costs.
Assuming we had a communication means with all the users and implementer/integrators (other than perhaps fiddling with the #ICANN section header comment or adding another one, which may break some people's code), and assuming some poll was assembled, and a subsequent polling period where we might get answers, would we still have a full list of use-cases? Likely not. We have made changes to the headers or structure of the file over the span of time and have rolled them back due to furious feedback from the community over those changes due to code breakage.
But lets, for a moment, assume we might get 100% of the use-cases so that we could potentially replace the current PSL process with a DNS-based solution that in fact may be a viable replacement. We already know of a few that don't, and it is statistically unlikely we would get all the use-cases reported to us, but let's ignore those factors for this hypothetical scenario and receive a solution that works for all of them from the IETF process.
Once one might conclude that expensive expedition, and let's for the sake of argument ignore that we know it would represent a viable solution, there is the matter of the labor, time and architecture, as well as costs involved in upgrading the systems to support it.
We have a lot of very burdened volunteers that are investing night and weekend personal hours in managing the current setup - with no spare cycles to feed into a process like those described above, which has the allure of stepping in front of a fast moving bus.
As a rule of thumb, as volunteers, want to support a robust system, but skip the expedition type activities out of a forced pragmatism that stems from our available cycles being dedicated to upkeep of this important internet resource.
We also apply that pragmatism as a full stop on DNS solutions for the time being due to knowing at least that X>1, so expedition = disposable labor. Also, expedition LOE > current LOE of basic (growing) upkeep.
"Upgrade" LOE also > current LOE . AND knowing X>1 means that there would need to be parallel evolution and reverse compatibility which expands the scope.
Some of us have invested time into (as has been pointed out) IETF process(es) that have not yet provided a viable path forward (John's most recent update to DBOUND is a little promising) and we have volunteered more of our time doing so in being as inclusive as possible about the known use cases being considered in the solution proposals.
Each iteration of these "let's DNS this" extracts volunteer time, which is something that we all try to approach with care.
John Levine made a recent re-proposal to the DBOUND, and as Dave mentioned, he recently proposed something as well. There are some areas where these could deliver some benefits using txt records in DNS, but largely to areas where the maintainers could pull self-identified records from authoritative zones via the DNS and incorporate them into the PSL static list. What I just described does not exist and would need to be developed, again, more volunteer time extraction that would be a likely non-starter.
If only those updates and changes would appear magically in a cornfield. Or, more realistically, there were a patron who would cover the costs and resourcing of the expedition and cover all of those costs and additional labor, people, time, etc of implementing those changes or the surrounding expeditions, it could be a potentially different outcome.
In the meantime, we try to limit the number of frisbees that we chase.
-Jothan