Well, let's start with the basics.
Radius:
1/8
3/16
1/4
3/8
1/2
Straight cut:
1/4
5/16
3/8
1/2
3/4
But..if you are trying to sell products to Festool owners, you might choose to offer a more comprehensive collection. So If you were to up the number to 20 cutters one might choose to include:
an Ogee or two, depending on what's available
a keyslot bit or two, for duplicating the side rails of an MFT
a Roman ogee or two
a wide mortising bit or two
a 5mm bit for the LS32
a 35mm bit for the LS32
a 20mm plunge bit to make MFT clones, or to bore some oddball hinge holes
And...if you wanted to virtually guarantee that all of us nerds on the F.O.G. would order one of your sets you might choose to include 10 more in any combination:
two or three edge profile bits for cabinet doors
one, two, or three different sizes of bullnose bits
one, two, or three different sizes of beading bits
one set of "shaker" or "arts and crafts" stile and rail bits for making doors
Then there are the more esoteric bit sets. Dovetail, patterned stile and rail, etc.
If you could sell one single set that 90 percent of retired hobbiest's like myself would buy to complete all the projects we pretend that we might someday complete.....you'd have it made.
I can tell you that if you were to put some sort of "monster collection" together the American boys would eat it up...and line up to send you 5 to 6 hundred dollars per set. You could subscribe to the Festool mentality of "put 20 important bits in a set, then include 10 that nobody wants and watch them all buy it"...or you could be the very first dude to actually build a truly comprehensive set of 8mm bits and watch them fly off the shelves.
Just my 2 cents.
J.