The width of the float not being fixed seems like a massive goal post shift. Unnecessarily so, honestly.
That said, this problem doesn't seem that much harder, honestly. Each float has a max size. They are only smaller if they had less text.
And see the example in the TeX-book. Basically a circular cutout for text aligned on a circle. Both parts fully hyphenated to fill the outline. I'm on my phone, but will try and find an example, if it would help.
Also, everything on the web is a rectangle, but that hasn't stopped people from hacking around this (https://meyerweb.com/eric/css/edge/slantastic/demo.html), and there is even a draft web standard to give shape to text (https://drafts.csswg.org/css-exclusions-1/), but only Microsoft has implemented it (https://caniuse.com/#feat=css-exclusions).