There’s a solution and it’s standardized bottles. And I have seen it implemented in a place I never expected: Kentucky. They have growlers (large glass containers with screw top lids) of standard sizes that are in common enough usage for beer that many shops offer a tap to fill it with beer and charge based on it. It’s one of the things I wish was more common elsewhere.

And as for metering, offer a price per unit mass (show mass of a glass) and weigh fill weigh pay.