URI_INTENT_SCHEME Specification
The method

Intent.parseUri(..., Intent.URI_INTENT_SCHEME)

http://developer.android.com/reference/android/content/Intent.html#parseUri%28java.lang.String,%20int%29

available since API level 4 allows to "serialize" essentially all of
an Intent instance data into a URI under the "intent:" scheme.

1) Is there an official, published specification for that URI scheme?

It doesn't seem to be listed on http://www.iana.org/assignments/uri-schemes.html

2) Are URIs generated with Intent.toUri() and consumed by
Intent.parseUri() stable/supported across API versions (supported in
future platform version)?
URI_INTENT_SCHEME Specification
===

The method

Intent.parseUri(..., Intent.URI_INTENT_SCHEME)

http://developer.android.com/reference/android/content/Intent.html#parseUri%28java.lang.String,%20int%29

available since API level 4 allows to "serialize" essentially all of
an Intent instance data into a URI under the "intent:" scheme.

1) Is there an official, published specification for that URI scheme?

It doesn't seem to be listed on http://www.iana.org/assignments/uri-schemes.html

2) Are URIs generated with Intent.toUri() and consumed by
Intent.parseUri() stable/supported across API versions (supported in
future platform version)?