I’m considering upgrading my speakers internal wiring

Go for it, I've been modifying crossovers and internal wiring for many years. One speaker manufacturer incorporated my mods in future production runs. Changing out internal wire, caps, resistors, inductors in crossovers usually results in easily heard differences. Determining exactly what you want to accomplish prior to mods important, research replacement parts to help ensure the replacements meet your needs. I also use the Duelund wire in my present speakers.

What the? This regular ol' speaker retails for ~18k??

Well, for what the dude charged you, he better already have put the best wire on earth, best crossover components. best of everything.

Curiosity killed the cat...luckily they have 9 lives.

I'd say scratch that curiosity itch - audiophile fun and likely better than a lifetime of wondering.  Seems like you can go back to the original wiring if desired.

Many years ago I re-wired a pair of speakers with what I thought was better wire. I loved those speakers, but after re-wiring them they sounded sufficiently different that I was never happy with them and I ended up selling them. Not only did they sound worse, I was constantly second guessing whether this was the way they were intended to sound. I have always regretted what I did to those speakers and wish I still had them in their original form.

You say:

I have a beautiful pair for PBN M1!5 in a Black finish which I love and sound incredible.

If you love them and they sound incredible, why on earth would you want to modify them? It is hard enough in this endless obsessive pursuit that we all subject ourselves to, to find something we love. In that rare moment when you do, try not to kill it. Even if you succeed in making it sound "better", it will still sound different, and that itself will be enough to drive you crazy. If you have an itch to scratch, buy some exotic power cable but please leave the speakers alone.

Thanks for all the input. I’m still on the fence. Also the fact that they sound great nor… upgrading the final 2 feet to the speakers themselves should Improve the sound further. 
Kenny I did not pay 18k for these. Reach out to Peter himself and get pricing. They’re worth every penny