Stefan Brands has created a fun way of distinguishing personal digital identity systems from enterprise federated identity systems - he uses a transportation analogy and classifies personal digital identity systems such as FOAF and LID as bicycles whereas SAML and Liberty are jet planes.
Under this taxonomy, I see LID as a unicycle - novel, but impractical and limited to people with a very specialized set of skills. As has been dissected in numerous other places (most expertly at Burningbird), LID's dependence on URLs as an identifier misses the mark in a number of ways - like a unicycle, LID is just not a useful way to get around.
SXIP would then be a Cessna - complex enough (with its hosted identities and 3rd party assertions) that you need a pilots license to use it, but not rigorous enough for a broad set of air travel requirements (e.g. SXIP is not based on standards).
The net/net of extending Stefan's metaphor this far....the status quo is inadequate and ripe for innovation on a number of fronts.