Not that I'm a Typescript fanboy, but it does have some nice features.
Aside from types, Typescript gives javascript the advantages of a compiled language. That helps preventing silly mistakes or oversight before even starting the test process.
One other really nice feature of Typescript as a programmer is beeing able to compile to older versions of javascript, allowing you to code with the latest standards while still having your script compatible with whatever environement you put it in.
That beeing said, I agree that It likely won't happen for MZ's engine (I'm not even sure if they took the time to rewrite it to ES6+ standards considering MV's code was mostly a copy/paste of previous versions), and It's up to everyone to work with whatever they're comfortable with.
I actually look forward to having the MZ using ES6+ or even TypeScript as well.
The changes from VXA to MV involves changing the language from Ruby to JavaScript, which is big enough for many VXA scripters not knowing JavaScript(including myself) to hesitate to just jump in(it took me 2 months to be comfortable with JavaScript), so I think it's just a special case for many MV codes to be copied from VXA codes, otherwise MV would risk scaring off too many VXA scripters from adapting to MV soon enough.
After all, largely copying the codebase from VXA to MV can help at least some such VXA scripters to pick up JavaScript and the MV codebase more quickly, and MV don't want to have too few plugin developers early on.
On the other hand, as long as MZ's really written in JavaScript, I expect a drastic codebase improvement(but I don't want to talk about any of the nontrivial MV codebase design issues here), due to the fact that
MV plugin developers don't have to learn a new language to work with MZ, unlike what VXA scripters not knowing JavaScript had to face when adapting to MV.
I personally consider adapting to ES6+ from ES5 to be a drastically easier, simpler and smaller task(it just took me 2 weeks) than adapting to JavaScript from Ruby, and those not going to adapt to TypeScript can just ignore it entirely, as
TypeScript is totally optional.
What's more, I expect some MZ plugin developers to be new to RM. Regardless of whether they know JavaScript, I'd guess that most of them will prefer ES6+ over ES5. Also, given the popularity of TypeScript, I feel that using TypeScript will increase the number of MZ plugin developers.
Of course, if the MZ codebase's indeed largely copied from the MV codebase, I'll still consider adapting to MZ, even though I'll really, really think twice before just jumping in
