It appears that #keyoxide claims can only be added for a fixed set of "platforms" and the keyoxide code needs to be modified to add further platforms. This seems inherently centralised. I wonder if it would be feasible to support a more generic approach to claims which would not need to be hardcoded into keyoxide? I guess the platform-specific aspect is being sure that a particular URI points at something which is owned by a user who may be asserting the claim.