So, to try to summarize, what's being suggested here is some mechanism for the user to activate reflowing zoom (i.e. the kind of zoom that Ctrl+Minus does on desktop, where we reflow the page contents into a different width) on mobile.
Two use cases have been presented:
Use case 1: On a small number of websites which are not designed with mobile devices in mind, the page layout can be very crowded without the ability to reflow-zoom out, making the page difficult to use.
The sort of website that's affected has been described as follows:
it tends to be niche non-IT company pages that are badly done and badly tested, which you usually need once in a lifetime but when you DO need them it tends to be quite a showstopper that you can't use them at all
The only current example that has come up so far is http://bibliothek.carl-schurz-haus.de, though it was mentioned that a past version of discordapp.com was affected.
Use case 2: When connecting an Android device to a desktop monitor via HDMI, then on most websites the screen space is under-utilized and page elements are very lage. Being able to reflow-zoom out would allow the browser to better utilize the larger amount of available screen space.
In terms of a mechanism for activating reflowing zoom, two suggestions have been made:
Mechanism 1: A setting in the hamburger menu (likely in the "Page" section) to increase or decrease the reflowing zoom scale. It could be similar to the "Zoom" entry in Firefox desktop's hamburger menu.
Mechanism 2: Have the pinch-zoom gesture, which triggers the mobile browser's current, non-reflowing zoom, start to trigger reflowing zoom if you're zoomed out to the smallest zoom level that's currently allowed, and you continue to perform the gesture. This could be accompanied by some sort of UI affordance to indicate when you've reached the limit of non-reflowing zoom, so that if a user doesn't wish to proceed to the reflowing zoom phase, they know when to stop pinching. (A specific suggestion for such an affordance was made here.)