I bought my MKII when 9.x was out. My AxeFX downloads folder on my computer shows 82 different firmware updates.
I've seen the introduction of scenes, ultra-res, new reverb, phaser, chorus, and delay types, reworking of the rotary block, doubling of user cab slots from 50 to 100, addition of about 30 more factory cabs, output meters, x/y states added to several blocks, plus numerous little tweaks that make things easier to use (like the grid display showing if a block is x or y, the 'move' grid screen showing which block you have selected, wrap around scrolling on the grid).