The presentation just mentioned “UXP won’t be a full browser, and web capability could by solved via Hybrid Plugins”.
Is there a guide for Premiere, what are the actual web capabilities, and best practice to extend this in case parts are missing?
I think you’re looking for WebView, not necessarily Hybrid Plugins. Using a WebView UI will give you full HTML/CSS/JS DOM support, so basically anything you can do on a website you can do in a UXP Plugin with a WebView UI.
UXP has a WebView widget you can get started with. We also have Bolt UXP which makes the entire WebView setup super easy and type-safe for single or multi-panel plugins.