Hang on… OF shows due tasks in a calendar app (if you turn that function on) and reminders have an alarm, and should not go into a calendar anyway so not sure where your issue is? Plus of course you can share calendars. If your trying to use OF to collaborate on projects its the wrong app!
Taskpaper is not dead, just mature, it basically works as is, and its a “language” (in a very basic sense) not a proprietary format like OF or Word, will it die? Possibly nearly everything does, and that includes OF, Wunderlist Things (if not already dead), 2Do etc etc.
No one forces TP format on anyone, there is a perfectly good UI built into OF for entering tasks in a natural language way, and I can send mail, URL’s text clippings etc to OF via the share sheet perfectly. OF tends to be one way though, get it in, do it, not sure what you want to “share”, as I said its not a collaboration tool.
Natural language in OF is a completely different thing than natural language in fantastical, but I am not sure if your talking about natural language in or out? Out could be done if its not already I am sure, in is very different. A quick scenario, two lists called finance, one in a personal folder, one in Business, trying to cover all bases would very quickly subvert any attempt at natural language, unless it was at a very basic level, and then people would be shouting for details, tags, due dates etc.
Basically Devs can never win, (some) users are never satisfied, a simple fact of life