> How would you all react to a (non-Slavic) Cyrillic-based
> alphabet using upside-down Cyrillic {s} and {z} for /T/ and
> /D/? The idea is that a 19th century alphabet maker was able
> to turn existing lead types upside down to create new
> symbols, but not to add diacritics or wholly new shapes.

What was easy for lead printers, that is not so easy for computer printers.
I wonder why Unicode does not have an "upside-down modifier".
For the lower-case upside-down Cyrilic <z> can be used Greek <e>, but the
other three glyphs are not available in usual fonts as Times or Courier.
But for example in "DejaVu" font, there is available U+0186 uppercase opened
O, suitable for your upside-down Cyrillic {s}, and U+0190 uppercase opened
E, suitable for your upside-down Cyrillic {z}. The lower-case characters are
U+0254 and U+025B.

P. A.