TW v5.3.8 currently only uses uses ES5 (2009) JS features, to work with old browsers.
With version v5.4.0 we intend to allow Javascript specification ES2017, which “allows” a lot of newer features. There are some JS features, that would be nice to use, which belong to ES2020, which was ruled out by the veto of Jeremy.
So the real question in this thread is not to use browser spec from 2024. IMO the question is, when to use ES2018, -19 and -20
I suppose such changes won’t break Tiddloid any time soon? I’ve recently had the opportunity to try using TiddlyWiki on a phone much newer than mine and the save time of my biggest encrypted wiki went from almost 30 seconds to like 2-3. Needless to say I’m euphoric (and said state shall persist till autumn 
).
Tiddloid uses the system WebView, which depends on the Android version and whether it receives updates anymore. (And so we go right back to the initial question.) But 10x speed gains are more likely to be from advances in mobile CPUs. Modern devices are being made increasingly faster.
It never drops to zero, but does it drastically change shape? ie, would a “support 9 year ES version but not newer” policy always be 5% left behind?.
It’s a genuine question - I don’t know. My gut feel is that in the short term the shape may change a little with more falling behind, but every now and then you get circumstances that provide extra impetus and pushes some of those that cling to move to something newer afterall. The example that springs to mind is the big shift to universal SSL over the last decade - which in turn makes me wonder if “the expiry of trusted certs built into a device” would make a reasonable metric for support? (it’s imperfect, given browsers can provide their own trusted certs, plus trusted root certs expire at different times, plus discovery of all that info for any given device!)
But Jeremy was suggesting that one-half of 1 percent was too much.
Over time I would expect that whatever the number is (2% ?) that it will grow with time. Because there will continue to be people and companies that hang on to particular technologies. Somewhere out there, someone is using Netscape Navigator.
The author of “What technology wants” says that no technology ever goes completely extinct. He reviewed a Montgomery Wards catalog from 1894. Taking a page about agricultural tools, he found that every single item was still being made and used somewhere (Although maybe quite a few were being used by the Amish).
I just came across a job listing where they still wanted people to know COBOL, which I thought would have been retired after all the Y2K fixes were complete.
I could freshen that up a little.