Honestly, I don't think Crabman really plotted much out in advance.
The Harem are a mix of the different cliche styles of girls but most of them either deliberately or by their characters are out of the waifu race from the start.
As said, Mero isn't wanting it, Suu and Papi are made too childlike to be serious contenders, Rachnee is too detached, and Lala is waiting for him to die. And if the big twist is supposed to be that he ends up with Smith (either human or succubus) it's a cop-out to the whole contest.
So for a supposed 6--way harem contest, it's really just a battle of Miia vs Cerea, and that doesn't really leave a lot of plot possibilities.
Hence why we get the MONgirls dating arc, and now the Farmgirls arc.
Crab can create and draw great characters, but it looks like there never was an overarching plan to go from Issue#1 all the way through to some future waifu ending.