I'm not sure if I'm not explaining myself or whether we're talking something different but what I meant is while Fuji might have a lot of different body 'systems', the updates go in chronological order, so for example XT1, XT2, XT3, or XE1, XE2, XE3 etc.
The only exception I can think the X100 series didn't follow a logical sequence but it's just they use the letter of the generation rather than number, so X100, X100S (second), X100T (Third), X100F (Fourth) but then they had to revert to roman numerals because if they followed the same nomenclature it would have been another X100F
I guess you could argue that's confusing, but at least it still goes up in numerical order, unlike the A6xxx series