It certainly is an expensive challange, and it may go for a year or more before someone ultimately takes the title out - but the main idea is to see how people go about things differently, and how the various mazda engines respond to severe NA modification.
The KL may cost more in terms of lack of aftermarket support, but the engine itself has lots more potential than the FS. Short stroke makes the thing an absolute rev monster, and the ability to push out 2.7L when overbored makes it a formidable engine.
In order to get the FS to have the same sort of potential as the KL, lots more needs to be spent on bottom end work to bring the stroke back to a level that is more able to rev to the limits that it will need to go to to break the 100whp/L mark. So all in all it comes out about the same.
The thing is, what ever way you go, theres going to need to be more custom bits than you can poke a stick at in the engine bay - and anyone competing in the challenge will likely end up with a very unique machine. I doubt that 2 people will approach the problem in the same way.
My advice? do loads of research, then spend thrift - go after the big areas of improvement first - the places where your engine of choice fails miserably. Fix those problems first and put the motor at the level it SHOULD have been at when delivered from the factory. Then try and win the challenge by doing the major modifications that are required to get you there.
Oh and you'll all need engine management to do it
put something on your shopping list