With the new Web Share Target API you can register your progressive web application as a share intent on Android devices. This is supported on mobile Chrome from version 71.
It's Happening! True USB input and output has been one of the most requested and completely neglected features missing from Android. With Android 5.0, it's finally arrived! Let's take a look at a Shield Tablet hooked up to a USB Mic!
Post Kinds Bookmarklets
Since you have the Post Kinds plugin set up, you might consider using that for a lot of the distance it can give you instead. I’ve written up some basic usage instructions for the plugin along with screenshots, but you’ll probably be most interested in the section on Bookmarklet Configuration. I’ve created a dozen or so browser bookmarklets, with handy visual emoji, for creating specific bookmark types for my site.
As for mobile posting, I’ll mention that I’ve heard “rumors” that David Shanske has a strong itch for improving the use of Post Kinds with a better mobile flow, so I would expect it to improve in the coming months. Until that time however, you can find some great tips on the wiki page for mobile posting. I recommend reading the entire page (including the section on Known which includes tools like URL Forwarder for Android that will also work with WordPress in conjunction with Post Kinds and the URL scheme described in the Bookmarklet Configuration section noted above.)
Using these details you should be able to make bookmarklets for your desktop browser and an Android phone in under an hour. If for some reason the documentation at these locations isn’t clear enough for you to puzzle out, let me know and I can do a more complete write up with screenshots and full code. (It’s still a piece of the book I need to expand out, or I’d include it here.)
WordPress has the option of setting up an email address by which to post to your site. You can configure this pretty quickly, especially for mobile use to send URLs to your website that way. I typically use this method for quickly bookmarking things to my site for private use at a later date.
There are also services that do bookmarking and include RSS feeds to your content which you could also potentially use to trigger IFTTT.com actions to post to your website. I have something similar to this set up for Reading.am which I’ve described in the past. You could certainly use this in combination with Diigo, which I see you use. Again, here more often than not I use these methods when I post things to my site as drafts or private posts.
Preparing for and reacting to Apple implementing your app’s core functionality themselves.
Upshot: Cover the 3 sigma edge cases that the bigger corporation won’t bother to support.