This is a tricky question:
Does CSS transition with fonts work with font-weight and font-family?
See for example:
https://www.cqrl.in/dev/font-transition.html
This is actually a Donald Knuth MetaFont question that will make Douglas Hofstadter smile!
Is there any hope of doing it through Canvas/SVG/SVG-font or some such thing?
If you think of them as curves it is topologically a simple homotopy deformation.