Only some minor things here:

— Section 3 —

   Although modern implementations have not strictly adhered to the 33
   millisecond interval, it is commonplace for implementations to limit
   the flooding rate to the same order of magnitude similar as the 33 ms
   value.

This sentence seems ungrammatical.  I think I know what you’re saying, so perhaps this will work?:

NEW
   Although modern implementations have not strictly adhered to the 33
   millisecond interval, it is commonplace for implementations to limit
   the flooding rate to the same order of magnitude: tens of milliseconds,
   and not the single digits or fractions of milliseconds that are needed today.
END

If that’s not quite right, please riff on it as appropriate.

— Section 4 —

   For a parameter which
   has never been advertised, an IS SHOULD use its local default value.
   That value SHOULD be configurable on a per-node basis and MAY be
   configurable on a per-interface basis.

Nit: I think the first SHOULD here ought not to be a BCP 14 key word, and only the second is.  I would write the first part of the sentence as a fact, and only have the second be a directive:

NEW
   For a parameter that
   has never been advertised, an IS uses its local default value.
   That value SHOULD be configurable on a per-node basis and MAY be
   configurable on a per-interface basis.
END

— Section 4.4 —

   Length: Indicates the length in octets (1-8) of the Value field.  The
   length SHOULD be the minimum required to send all bits that are set.

The SHOULD seems very odd: what would be a good reason to make it longer than necessary?  Is there a real reason not to straightforwardly say, “The length is the minimum required…”?

— Section 6 —

Just a “thanks” comment here: I found Section 6 and its subsections to be clear and informative.

— Section 8 —

I think the additional implications of having the new TLV have been well thought out, and I don’t see anything missing.