In chicago and burbs, there is very little NM. The boxes are all hard piped, this makes changes a little more difficult. Of course it makes it easier to repull new wires. But a homeowner isn't happy to hear they have to rewire part of the house to change out a light fixture.
Now the other question is, does the listing require the wires connected to the fixture wires to be 90C or all the wires in the J-box? When the J-box is part of the assembly of the fixture such as can lights, I can see it, but a j-box mounted in the ceiling? If it is just the connected wires, then add some new pigtails to the old wire.
If the old insulation is falling off the existing wires, then it is not really insulation anymore and must be replaced anyways.
