Tinker What do you mean by "it won't go anywhere"? It has already gone somewhere. It's here and has been for some time. Tens of thousands of people are happily using SL sets of irons and that number is growing. And I think that it is just in its early stages of mainstream recognition. I still talk to a LOT of golfers who have never heard of the concept or do not understand that it is an option for them. Almost every time I correct someone on this, their response is "Wow, that makes so much sense. I'd love to try a set of those. Where do you get them?"
Now, if by "it will go nowhere" you mean that SL will never makeup the largest part of the market, I may agree with you. SL will get lost as people chase this year's "sizzle/buzz." But I'm not willing to say "never." I can see a scenario where these clubs grow increasingly popular with new golfers: they are GREAT for beginners. In that scenario, people are unlikely to switch away from them as they move forward in their golfing careers. However, this will depend on them having more models to choose from. If the model options do not grow with the popularity, even these golfers will probably succumb to the "buzz hunt" and move to a multi-length. So, I agree with you that as long as the OEM stay away from SL, they will always be a niche (a sizeable niche, but a niche nonetheless).
(BTW, why can you not imagine Phil flopping a 37 or 37.5" wedge? He can flop a 36.5" wedge, but not a 37 or 37.5"? Wow, Phil, hit the range. If I can flop a 37.5" wedge, Phil probably can. And even if he can't, have him call me and I'll explain the concept of "choking up" to him.)