No, it was more broad than just SE domains, but trying to detect whether a site is suitable for passkeys support automatically is quite the challenge. Some don't allow themselves to be crawled so require manual verification.
I can kind of see it, but you can also just use an authenticator from any manufacturer, or have multiple types that you use? I'm just curious what I'm overlooking.
We had an expensive solar install due to restrictions around our roof, so the solar would typically have been cheaper.
Another consideration is that battery installations in the UK are charged at 20% VAT, but if they're installed as part of a solar installation, they're charged at 0% VAT. So even if your main interest is in getting the batteries, a small solar install might make sense because of the savings.
The only restriction placed on you is the export rate, which is provided to you by the DNO here in the UK. We had a limit of 3.8kW placed, which is programmed in to the batteries by the installer.
They're all 3 certificates long (leaf/intermediate/root) apart from Let's Encrypt which, due to their cross-signature, are 4 certificates long for ECC.
If you were to use the same private key for the 4 certificates then you could seamlessly switch between whichever leaf certificate you wanted to serve to the client. I'm not aware of the ability to send multiple leaf certificates to a client for consideration though.
If you get a 1 year certificate then yeah, but otherwise no. The requirement to re-validate the DNS record comes not from the CA or the use of ACME, but the Baseline Requirements[1] §4.2.1, to prove you are still in control of the domain on a somewhat regular basis to obtain new certificates. Every 3 months is more frequent than is required, but there is still a regular (398 day) DCV requirement.