I have only minor comments.

The section said that security issues in this document are mostly inherited from the underlying techniques/specs.
Some pointers to RFC documents describing the security issues of MPLS dataplane, routing protocols, and so on (if any) could help readers.
Having these pointers in this section will not harm readers.

Some typo:
In Section 1: "co- exist" (unnecessary space)-> "co-exist"
In Section 2.1: "switches it our" -> "switches it out"

Spelling out is appreciated: LDP and FEC 

Clarification question:
Regarding the paragraph "P6 does not have an LDP binding from its next-hop P5 for the FEC "PE1". However P6 has an SR node segment to the IGP route "PE1". Hence, P6 forwards the packet to P5 and swaps its local LDP-label for FEC "PE1" by the equivalent node segment (i.e. 101)."(in Section 4.1), I have got the impression that the behavior of P6 is not defined by any other specs (incl, LDP) and is a behavior this document newly defines, correct?  If it is correct, must P6 support this behavior? or is it just optional? I am not familiar with these routing protocols, thus clarification is appreciated.