I think pluv speaks for me here too. I thought the 2.5 line was a cool idea, but I had no interest in replacing everything I'd bought at that point with an incompatible scale (especially considering I didn't really have the income then to consider it seriously). A separate scale requires separate display space, which is also something I simply don't have. I think my experience with the gap between the last DTC six-packs and the debut of the 25th line taught me that if there are no 3-3/4" or 4" offerings available for purchase, I simply won't buy anything.

Another problem with any new scale or line is what Scramble mentioned - there's simply too much focus on a small core group of heroes and a terrible under-representation of villain/enemy characters. G.I. Joe has been fortunate to keep a reasonable ratio of heroes to villains, though the core characters do get seriously overused. Even if that model is fully embraced for Joe, I still have enough existing compatible figures to make up for the difference. That is not an advantage for any new line, especially if the scale changes.

I liked some of the designs and looks of the characters themselves and the vehicles were pretty amazing, but the scale killed it for me. I collect Joe's to play with, and these simply did not fit with my vast ARAH army. I had a few but they never saw much use from me, and I ended up selling them off on ebay.
Had they been released as O-ring ARAH type figures in the 3 3/4" scale I would have been all over the concept, and toys.

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I'd only buy Sigma Six if they were built like ARAH.