> Very few languages can do all 4. JVM ones can't
Java can (JIT is trivial, for AOT there is among others Graal, for JS and WASM there is TeaVM (which works on class files, so now that I think about it, pretty much every JVM language can do all platforms), but also the very great Closure compiler (j2cl) which has no relation to cloJure, made and used heavily by google)
With your Java example, that's exactly what I mean, you don't need 4 different tools in Dart to achieve the 4 types of compilation, they're all included in the standard Dart compiler/SDK. Sure, if we go by your definition, probably any language has some level of support for each via various random compilers but I'm talking about something first-class, built-in.
While there is surely a very delicate balance of slowly deprecating a few things, remember that the only significant productivity booster is relying on existing code (as per Brooks).
I’m fairly sure there are orders of magnitude more Java code transpiled to JS running at Google than all of their Dart codebases combined, so not sure “random compilers” are a fair description.
Another thing is Dart is JITed, AOT compiled as well as compiling to JS and WASM. Very few languages can do all 4. JVM ones can't, so no Kotlin (we'll see how well Kotlin Native works), and V8 isn't AOT so no JS or TS either. Only alternative I can think of is Lua.