An additional element of my user fee / tax-based support, and one that strongly distinguishes it from a flat-fee assessment as with the BBC or German public broadcasting is that it should be strongly progressive.

For a tax assessment this would be based on wealth (e.g., property tax) and/or income. For an ISP-based assessment, the allocation might be more challenging, but a differentiation between business and residential usage (with a higher assessment for businesses, again on a progressive scale), and differentiated rates probably on a neighbourhood / metro region basis (so that a household on the Upper West Side and one in Julesburg, CO, would pay widely differing rates), is what I have in mind.

Rationale is that the wealthy have already benefitted mightily from such access, and the poor should not be denied access to media: news, entertainment, books, music, video, whatever.

You say "forced". I say enlighted common weal.