An important part of Ricardo Niemietz's hex digit proposal (http://std.dkuug.dk/jtc1/sc2/wg2/docs/n2677) is to have columns of hexadecimal numbers line up properly as columns of decimal numbers do. This could be achieved using a font with a set of glyph variants for A-F with a hexadecimal property. Such a glyph variant table could be added to, for example, an OpenType font. Then a display engine that encounters a text run with the hexadecimal property could request the hexadecimal glyph variants. This mechanism is similar to requesting old-style numerals when a document so specifies. Seems like a good idea.
As Mark and Ken have pointed out numerous times, changing other aspects of hex digits is fraught with compatibility problems. Thanks Murray
