1 Not expecting it… I’m sure they’re busy with an enormous backlog and this likely far outside the scope of many users / use cases.
2 I hate Javascript too so we’re aligned there 
Unfortunately, it’s what we have for client side web, and it’s more portable… so I work with it where / when I have to. In this case… we’re talking about markdown (or html) files… the whole point is they’re portable / future proof. That rules out Applescript / Shortcuts etc for me in some - many instances.
3 It wouldn’t be just for md files. In fact, it’s actually more relevant to html files. Md files just happen to translate a lot of html too. (And I only used md files in this particular instance because DTTG kept converting html files to formatted notes.) The point though is… SPAs. You could pseudo-host a web application within DT. That’s huge! It opens up all kinds of possibilities. But the single block right now (and I know it because I tried all sorts of hacks to workaround) is… from within javascript within a html document you cannot retrieve or save the contents of another document. If you could… you could use a html document UI (built yourself) as an interface to your documents… saving page / data states down to another document (either a json file, csv, or even sqlite db). Next time you open the html page… it reads from the other document and so on. Basically… a web app. Ta daa!
4 Yeah I’m sure it’s already challenging keeping things working coherently across both platforms. I’ve developed natively for iOS and Mac… I know there are significant differences. This might add another fork in the ongoing maintenance… but I’d expect it to be a thin layer providing the hook between the document file system and the browser engine… vs a potential fat reward for a library of SPAs they could then include alongside all the scripts and plugins and so on.
5 The js API in DT… are you talking about the Applescript alternative? If so, is there any way that code can be executed from within a html (or md) document via embedded javascript? I suspect not… in which case it’s not the same thing. As for whether DTTG could support this… unless Apple has changed / restricted the iOS SDK further, I remember seeing / tinkering with the capability of doing exactly what I’m talking about (event / messaging between safari containers and the native environment). There are a whole heap of other scenarios where that is needed. This one is not really that special?
There’s an app to save tiddlywiki states on iOS that does what I’m talking about… Quine. And of course… there is all those js plugins in that “other” app that shallt not be named Minecraft netherworld block ahem… they all interact just fine with the local app’s documents. Seems to me DT is only a thin layer away from the same prize of rich web-based plugin ecosystem?