You know the weirdest thought I had regarding this ending and how it was done is the possibility that "Shinsetsu" may have never actually happened. Outside the Beauty scene and the bit with the Kancho, it was all a big throwback to the original series: the Fist of the North Star world, the weirdness everywhere, only one Maruhage Empire force. Considering how "different" the world of the second series is (replacing the silly, imaginary FoNS towns with "Neo-Japanese cities", how modern and current everything looked), I keep debating whether Sawai had planned this from the beginning or if this was a "well Shueisha wants me to keep it going so here's my pt. 2" thing. If you could eliminate the whole "Tsurulina the Third goes to the Hair Kingdom" subplot (and thus keep Bi-bibi alive after losing to Bo-bobo), slighty adjust some things (have Beauty and Heppokomaru run off with each other at the end of pt. 1, thus needing to redraw that scene with their younger selves) and combine this with the final chapter of pt. 1, this could actually work better as a more complete and interesting finale without acknowledging that Shinsetsu ever happened. (heck the pt. 1 ending even gave a finale to Softon, Hatenko and Dengaku Man, so it would work to their advantage too)
Another interesting thought I got from this ending: somehow I'm starting to think that Don Patch isn't merely a Hajike boss but could literally be "the god" of this weird, wacked out world, choosing to ride along with Bo-bobo to the end. Sort of a combination of a Greek and Norse being of power: manipulating yet also slightly mortal himself in an immortal way.