Guilt not needed.  ran a poll but the numbers were decidedly against. Will revisit

Spanner slots or wrench flats? Wrench flat version will be heavier.

Looks fantastic!  I should have our prototypes in the coming weeks.

I think the reason they aren't more popular probably has something to do with:

1 the specialized nature of a taper mount that could confuse other 1/2x28 customers or 5/8x24 customers, leading to issues and returns with the majority of customers
2 the fact there is a work around (taper shoulder ring)
3 the additional ~.12" of depth is at odds with indexable thread mills in 1/2x28 which can't really effectively reach that depth with rigidity
4 that indexable single point thread tools aren't very process stable in blind holes where that geometry should get cut
5 blowing up sku counts for relatively little need is never appreciated by vendors and doesn't enhance the efficiency of production.  

There are work arounds- like ordering special solid carbide thread mills for this part, or rigid tapping which sounds like a pretty bad idea in 17-4. But that's now point 1, 2, 5 and point 6 additional tooling required so more crap to juggle in the factory making the part.  

We would probably have done it if the thread were comped for the additional length like .630 becomes .510 thread length on account of the need to keep the hole ID work tight in small threaded holes.  The Sig engineers probably didn't do that because they wanted backward compatibility with the tapered shoulder rings, understanding customers would be buying their rifles for one of 15 or so brands of silencers that had minor significance and would be annoyed if there was no compatibility at launch time.

Single pointing on a CNC machine, the tool we (rarely) use for that is like .470 min bore, and we're running it in a .458 hole, so it's tight, the holder isn't that rigid even being larger than ideal for the hole, and the chips get recut sometimes and trash inserts at low life sporadically, so the jobs don't run well.  Tap magic is really nice, but we would have to count on water based coolant for tapping (automatic coolant) and I think that's asking a lot of coolant because that's going to be a very hot application, but I haven't actually tried tapping so I can't say it wouldn't work.  Sometimes something you don't do and are concerned about is no issue, and sometimes the concerns were valid and it's a mess.   We have done thread milling of tiny holes with solid carbide and it works fine.  I'm sure thread milling with solid carbide would work, it would just also be abnormally expensive in cost of that one operation per part, and would require special tools which isn't by itself all that big of a deal.  

Maybe we should eventually support tapered shoulder barrels in a muzzle device.  I don't really see why they should take off though given most suppressors are mounted to muzzle devices.   The really strong positive attribute of tapered shoulder barrels would seem to be temporary direct mounting and dismounting cans with no muzzle device, which leaves the expensive, difficult to replace, barrel vulnerable to damage when the suppressor is removed.  It's a special new thread for applications that already have a standard and the parts already work without tapered shoulders, and the tapers do eat useable shoulder on thin barrels in backward compatible applications with existing barrels.  You may not even technically need a taper shoulder ring if you use a muzzle indexing flash suppressor with a tapered shoulder barrel.  I get that there is some slight improvement theoretically in the tapered shoulder, but it's non-standard.