Nick Shinn

What Mark said.
I use <command shift h> in InDesign—very clever and useful, and can even be executed with one hand.

Dear me, whatever happened to poor old Caslon?!

I expect that type designers will continue to implement various forms, as they have with the Euro, but the form(s) used in the most prevalent faces (ubiquitous through popularity or OS distribution) will become prevalent, irrespective of the merit of their Eszett.

The default shown on the Unicode code page may have some influence.

I think you would be better off working on a sans. Serifed fonts are not very popular, as you predict, and this one seems to cover no new ground.
  
But if you are determined: What does Caster introduce that does not already exist in, say, Zapf International? (In the basic alphabetic design, not language support or OpenType features such as figure alts.)

Certainly, it is original, but not enough—because, in sans faces, people are more attuned to the significance of subtle differences, which they just don’t see in the old-fashioned serif genre.

Now you might say, serif fonts will come back into fashion; but that won’t help typefaces designed premature to such an event, should it happen. Timing is everything when it comes to trends.

On a positive note, bravo for doing size-specific variants—that is a saleable feature, especially if embedded in the hot new format of OTVar.

What about W?
I_J?