Greek Fonts (variant character forms)

There are several issues involved here.

1. How you should encode (e.g.) a sigma in the web page or database so that you can find 3-bar, 4-bar, lunate etc. sigmas using a single search, say for ΣΩΖ-. The answer this is emphatically that the Unicode character for sigma should be used, rather than (say), something that looks like the 3-bar sigma such as the lightning-bolt koppa at U+03DF.
2. How should you display a lightning-bolt shaped character on a screen or printed page? Ideally the answer would be to use a font with variant form sigmas (see 3. below), but while waiting for this to be implemented, one might decide to use a similarly shaped character from a different codepoint for display only.
3. How to indicate via markup that a particular sigma is 3-bar or 4-bar or lunate, vel sim., in such a way that a web browser/document printer etc can extract and deal with this information thus printing it correctly on the scree/page? It is possible to encode an OpenType font with multiple glyphs for any given character codepoint (so multiple variant sigmas, epsilons, alphas, etc.). I'm not quite clear yet on how this is going to work, although I believe Dumbarton Oaks are working on such a font for sigillographic and epigraphic puposes. It would be good to get their feedback on this.