Why not 2 or 3 different width dominos in each size?

It sounds like a good idea for some applications although if doing a row of mortises there would be no allowance for error.
 
I've got a bunch of stock cut for 8mm and 10mm on the wide setting.  I make them a little bit looser than the Festool tenons because mine don't have indentations for glue..

Consider also that you aren't limited to the wide setting.  You can make a mortise any width you like using multiple plunges.  If you have the pin type fence you can use it to register all sorts of widths by using both extremities in the first plunge.
 
actually not a bad idea, i think i will make some for the 8 and 10 as well. though i am a bit afraid of loosing some accuracy as the domino is harder to control in medium and wide setting.
 
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