Despite what many folks will claim based purely off older out of reach things being automatically more desirable to many, with the addition of the vintage knob I actually think the OB-6 is the vastly superior instrument. On a more subjective note, I also think the OB-6 is aesthetically the better looking of the two and it's not the size of a house. Furthermore, Abstrakt Instruments has a module version (with Tom's blessing supposedly) called the VS-1. The only real plus I see the OB-X having is five octaves.
While also not what I want, I thought the OB-Xa or OB-8 would have gained more intrigue because while they're not as highly regarded to the purists, they're more iconic to the masses. Plus they have the same available components (the VCO and VCF) as the rev 3 of the P5 (that's in the rev 4), which would more importantly for Sequential's line-up compete less with the OB-6. The crazy thing is how much both (Xa/8) sound much more Oberheim (sharper/buzzier) than a P5 clone, despite having the two major components that many people consider what makes up the majority of the character. I suppose having both the OB-X & OB-Xa/8 filters would make sense given the P5/10. I actually found myself using the 3320 just as much as the 2140 on the rev 4. I find that people vastly overrate things based on chronological priority, in this case the rev 1/2 over the 3.
It's my opinion that a knobby Matrix-12 rev 2 with the 3340 VCOs and 3320 VCFs (or dual SEMs that are 12dB and 24dB switchable) would be more tactile and better sounding than the original. Plus the foundation is already there from the REV2.