I have been tasked to review this document on behalf of the OPS DIR.  I wouldn't say I'm an expert in this area, but overall I found the draft easy to read, and from an operations point of view I appreciate the succinct applicability summaries, as well as the points to future extensibility work (though I wonder if those deserve their own section for added clarity).

On the nits side, I notice you compare your Figure 3 with the figure in Section 3 of RFC7138.  However, you omit the notion of labeling the A, B, etc. with "OTN Switch", which I think would help.  I'm also not sure what "3R" means here or in Figure 1 (but that is likely my lack of experience here).  Finally, the two parts of Figure 3 seem to be showing both one-hop and multi-hop OTUCn links but you do not call that out as is done in RFC7138.