Roadmap

Not really a roadmap, just a list of features and what will need to change to implement them.
This is just a reminder for my future self of what will be possible when/if these things are added. this may prove to be a useful resource.
Any one of the numbered items would be enough to make the preceeding feature possible, all are not required.

Parity with discord-chrome-app

Theme title bar to match appearance of desktop client

Chromium support for display: fullscreen in manifest.json may allow this.
Chromium support for chrome.app.window in PWAs would allow this through frame: none (this is how it is done in discord-chrome-app.

Hide status bar

Both fixes for the title bar would incidentally fix this, though I'm not 100% sure display: fullscreen would.

Run independently from browser extensions.

Already possible through the chrome flag #enable-desktop-pwas-without-extensions

Function solely as a PWA (no extension required) [very unlikely]

iframe workaround

Chromium would need to supply an api similar to webrequest for PWAs, specifically the ability to modify HTTP headers is needed.
Chromium should add something similar to a webview for PWAs, this would allow discord to be "embedded" without an iframe, the way discord-chrome-app does it.

Desktop icon highlight

Chromium needs to allow something like chrome.window's drawAttention in PWAs.