20 years is too pessimistic. It was nearly accurate exactly once, which is where IE6 remained dominant for nearly a decade and a half. As far as anyone can tell, there will probably not be another case where a single outdated version of a browser contains a significant part of the marketshare. Most folks are now using browsers that update automatically, be it Edge, Safari, Chrome, Firefox or even numerous niche browsers.
There of course remain some demographics where outdated browsers live on. Like I'm sure the last version of Chrome that works on XP has some marketshare in China.
The worst case I can really think of is older Android, but let's at least keep in mind that Android has only been in people's hands for a decade, and practically speaking most developers are not very concerned with supporting Android Browser from really old Android releases. IIRC, Cloudflare's free tier already doesn't work with Android Browser from 2.2 because at that point it didn't support SNI. Not to mention, Android Browser marketshare is quite tiny at this point, as I believe Chrome or Samsung Browser is usually the default browser on modern Android handsets.
I would guess as long as this move goes off without a hitch and isn't reverted it will likely be the safe reality in under 5 years. My guess is not particularly special, but I mean, the internet is already unusable on really old browsers. For better or worse, the world we live in doesn't have much tolerance for older software versions. Sometimes this is for pretty good reasons (such as improving cryptography standards.)
I will admit I have a strong aversion to breaking browser support for anyone pretty much, but the security of 95% of users is worth forcing 5% of users to update their damn software. It's unfortunate that the situation can't be a bit more backwards compatible, but I think that's just how things go with certain hard problems. There's never not going to be some compromise, and it doesn't seem likely any time in the future will be particularly better than right now.
There of course remain some demographics where outdated browsers live on. Like I'm sure the last version of Chrome that works on XP has some marketshare in China.
The worst case I can really think of is older Android, but let's at least keep in mind that Android has only been in people's hands for a decade, and practically speaking most developers are not very concerned with supporting Android Browser from really old Android releases. IIRC, Cloudflare's free tier already doesn't work with Android Browser from 2.2 because at that point it didn't support SNI. Not to mention, Android Browser marketshare is quite tiny at this point, as I believe Chrome or Samsung Browser is usually the default browser on modern Android handsets.
I would guess as long as this move goes off without a hitch and isn't reverted it will likely be the safe reality in under 5 years. My guess is not particularly special, but I mean, the internet is already unusable on really old browsers. For better or worse, the world we live in doesn't have much tolerance for older software versions. Sometimes this is for pretty good reasons (such as improving cryptography standards.)
I will admit I have a strong aversion to breaking browser support for anyone pretty much, but the security of 95% of users is worth forcing 5% of users to update their damn software. It's unfortunate that the situation can't be a bit more backwards compatible, but I think that's just how things go with certain hard problems. There's never not going to be some compromise, and it doesn't seem likely any time in the future will be particularly better than right now.