Overall:

The document is well-written and almost ready for publication

Comments:

1) No examples or guidance for "encaps-type"

The document does not really define the standards value
for this empty choice.  There are no examples showing its use.
More work is needed for this part of the module.

The following TODO needs to be resolved and the note removed
from the document:

           /*
            * TODO - Should we introduce an abstract type to make this
            *        extensible to new interface types, or vendor
            *        specific interface types?
            */

2) normative overlap

The text and layout of sec. 3 is good.
The issue is that the YANG module text copies from this section
in some places (leafs) and references it in others (feature definitions)

Some parts like "half-life" are more detailed in the leaf definition
than the plain text in sec. 3

Perhaps the leaf definitions can have reference-stmts added
as needed, so it is clear that the YANG leaf is not the
entire normative text.  The YANG descriptions are good,
but maybe not complete wrt/ sec. 3 additional text.


sec 3.7 typo:

the existing the sub-interface
                    ^^^  remove extra 'the'

3) identity ethSubInterface

This identity is used in the encapsulation container when-stmt.
It is not clear if this is intended as a base identity (like identity
sub-interface)
An example for the encapsulation container would help clarify the
expected usage

This also has 2 bases (sub-interface and l2vlan).
Some explanation in the identity-stmt would be helpful
(since this is a new YANG 1.1 construct)



Andy