[0] https://tools.ietf.org/html/rfc6698DANE definitely does not "work" for SMTP.
The necessity for DNSSEC in SMTP is, I think, a desperate trope† that recognizes that the Web PKI has moved past considering DANE and begun investing in direct hardening for the X.509 system. SMTP is other mainstream protocol for which transport security couldn't be guaranteed, is mired in the late 1990s technologically, and doesn't inherit modern browser- and server- based protection. So: SMTP! SMTP is the reason we need DNSSEC! We must get DNSSEC deployed immediately so everyone can have secure SMTP!
Except, you know who doesn't agree with you? The people who the most important email services. Hence: MTA-STS --- a standard whose introduction spells out its raison d'être: to avoid DANE! --- and the mooting of that last fragile argument for deploying DNSSEC.
DANE is a dead letter.
† I'm choosing words carefully
No, the major providers did not get together to do MTA-STS because DANE was bad. They did it because their existing DNS geo-balancing kit for e.g. google.com and yahoo.com does not offer an easy upgrade path to DNSSEC. Note that Microsoft has a dedicated domain (outlook.com) for email hosting, and can more easily do DNSSEC there without impacting their other "web properties". Note also that Google now MX-hosts many customer domains on "googlemail.com" rather than google.com.
So things are starting to change. Furthermore, there are now over 1 million DANE-enabled DNSSEC domains. MTA-STS is far behind, is not downgrade-resistant on first contact and uses weak CA-leap-of-faith DV authentication. It will probably be enabled at the biggest providers by the end of this year, but as you yourself said elsewhere, these providers are the threat, and if so, securing email delivery to the user surveillance empires is not necessarily that important. Mind you, they can play a useful role by enabling validation and helping to keep the TLSA records of receiving systems valid, and perhaps surveillance is not their business for paying customers...
There are a million DANE-enabled DNSSEC domains because there are registrars, particularly in Europe, that enable it automatically. Who cares? First of all, DNSSEC managed by your registrar is security theater, but, more importantly, the overwhelming majority of those domains do not matter. Who cares if some landing page in the Netherlands has TLSA records?
Meanwhile, the domains that really do matter --- the ones managed by the major mail providers --- are doing MTA-STS.
SMTP is not a success case for DNSSEC.
Recall: the argument you're responding to (you drew it up from downthread) is that DANE "definitely works for SMTP". Does it, now?
Yes, only ~9 to 10 million domains are presently signed, and most of the larger ones are not (but comcast.net and cloudflare.com are not tiny, and gmx.de has over 10 million email users). Changing this takes time and effort. Users still need better software tools that make deployment easier and there needs to be less KSK deployment and rollover friction at the registrars and registries (i.e. CDS support). Some DNS hosting providers with outdated software need to upgrade their stacks, ... this does not happen overnight. Let's compare notes in 2020 or 2021. Infrastructure upgrades happen slowly...