Those bloody signed certificates are a menace.
This is precisely why OpenSSH decided against certificate authorities (by default).
Bashful booting or sneaky certificates – our hospitals are not immune from the perils posed by bork. We have a pair of medical fails today, one from a surgical recovery room in the US and the other lurking within the UK's beloved NHS. The first bit of bedside borkage comes from a Register reader in North America and shows a …
What is wrong with a system where the certificate never automatically expires, but can be revoked if & when necessary, is that you end up with certificates that are valid in perpetuity by default unless revoked. And it is a lot easier to block a "do not use this certificate anymore" message, than it is to create a plausible fake certificate.
What you are proposing is equivalent to a lock that can be opened using any tool, unless it has been specifically told that that tool is not the key that opens it.
...anybody's surprised at "dear old Internet Explorer" in the NHS. A large number of expensive browser-based applications only ran on IE of a certain vintage until recently. I believe manufacturers had to be threatened with losing the business before they would upgrade their software to run on more recent (read more secure) versions. Some still required IE (not Chrome or any other pretender) when I retired at the end of 2019.
What were the procurement people smoking, buying software without demanding Source Code (and the relevant Modification Rights to go with it)? Those are your guarantee, and you never let go of them!
Now, you personally might not know what to do with Source Code, and you might even take a perverse pride in that ignorance (which, as the sort of person who knows exactly what to do with it, actually suits me fine); but if the worst ever happens and the original supplier goes out of business, access to the Source Code at least ensures any competent programmer will be able to maintain it for you. (In fact, the original vendor needn't even go out of business; if they get a bit too big for their boots with ongoing costs, a customer with the Source Code can up sticks and go their own way, like a motorist going to an independent garage instead of a brand-tied dealership.)
If I was ever to break the habit of a lifetime and pay money for a piece of software, you can bet I would be insisting for at least the same Source Code and Modification Rights I would have got if I had downloaded a different piece of software instead that I would not have to pay for. "Pay more, get less" doesn't sit with my brand.
This is healthcare software. When only two manufacturers make the stuff you want and neither of them wants to play ball, you take what you can get. I've been involved in specialized software deployment at a coalface level, and honestly the bottom line is that you take what's available and shoe-horn your processes to fit that. And that goes from patient admin software to the tools required to mine data from the lab system. I could expand but I don't want to go further off-topic than I have already.