It is kind of amusing though, he can play with many pinsiders like puppets on a string. He seems to press all the right buttons.

That way he manages to get the attention he craves every time. Simply ignoring him would make him go away quite quickly.

This. If it's any good and priced below 7K it will sell very well. People are fed up with the ridiculous pricing strategy of the established producers - in any other market competition leads to lower prices, in pinball it seems to be the other way around.

Will there be a risk? I can't imagine AP wants to use any kind of prepay/preorder strategy. I can even less imagine any pinhead would be stupid enough to ever prepay any pin again.

But then again it's a small miracle to me that people actually prepaid stuff in the past, that business model was always a complete no-go to me.

It's actually not that stupid given this is a completely privately owned company. Of course it couldn't work if you have shareholders in it that demand quick return as they usually do.
If a designer, theoretically, is paid 200K at Stern AP would have to pay 300K minimum to get them to move to an unproven startup. And what would they have then? Most probably not Steve Ritchie or George Gomez but rather the second tier designers that are not really famous for pumping out jaw dropping designs. Good down to earth designers of course, but not mesmerizing ones. JPop managed to lure educated grown men into investing tens of thousands of dollars for games that could in no thinkable setting be produced profitably. So like him or not, there must be something special about his designs/visions. AP also have people on board that have proven to be able to work with him and turn is ideas into a product. And he is bringing 3 designs in different stages of completion plus the stuff he probably had in the pipeline for years (Houdini). If every game really would cost maybe 750K to develop, they already could have saved 500K each for MG & Houdini, 250K each for RAZA & AIW, so that's 1.5Million saved...money they can use to "make the old owners whole". Until the "whole making" part is achieved JPop might be working for free.
With most other designers (IF they managed to get one of them, huge IF) they would spend 300K p.a. and would have to start from scrap for the first, second, third and every other game. If it then takes them an optimistic 2 years to produce the first game they have spent 600K for the designer plus 750K for development of the game, so that's 1.35Million for a completely unproven risk as opposed to JPops designs everyone was slobbering over.
Of course this is complete BS as it's an incomplete calculation based on wild guesswork regarding the figures, but it might give you an idea of what could be APs motivation to collaborate with JPop.
The big question is what impact the Zidware disaster and Johns reputation will really have on sales of AP. Most collectors I know personally are not on any pinball forums and the ones active on forums are even below 10%. Do not underestimate how many collectors are busy people that have better things to do than spend hours reading lame carguments and kiddie fights on internet forums. If these guys go to their distributor and enjoy Houdini more than the machine next to it they will buy it. On the German forum I even had to explain what happened "back then" because some people didn't understand what the bitching was about when Houdini was announced.

There's a lot of ifs in this and it's a challenging plan to say the least, but bearing in mind that it takes the average company three years to break even it is possible that this might work if it was calculated conservatively.

I don't see the connection between "appointment" and "preorder"?

I would guess for press people, potential distributors, stakeholders like the Zidware customers, suppliers, etc.
Can't imagine there will be any preordering or prepayment process.
I'm assuming (hoping) they will just make games and sell them off the shelf, you know, the good old straightforward trustworthy traditional business model.