Thank you for the reply. Glad to be here.
Maybe 'glaring' is a bit heavy.... :-) I should point out where I am coming from. My interest in Tormach and other personal CNC machines is that I am trying to add CNC to my home shop. I have a small business (11 years) that does mechanical and electrical engineering with a few of our own products. I have been a machinist for 10+ years and owned 3 Haas machines, 2 of them 5 axis. Most professionals understand that Haas is the 'entry level' industrial machine. The don't suck, but they are not amazing either like Okuma and Kitamura, etc.... With that said - I have never even seen anyone use a tapping head other than the toolroom Bridgport maintenance guy. The reason is that rigid tapping is very predictable and allows you to go to the very bottom of a blind hole everytime. Tap breakage is very uncommon. We do parts with 40+ threaded holes of 2-56 and 4-40 which require no real effort or thought. Our go-to tap holders were the Techniks rigid tap and micro-float holders which are nice and short (not eating up Z travel for tall parts). I could tap at 1500 RPM / 27 ipm with 2-56 form taps which is really quick. The taps last for a VERY long time.
** The following are my understanding of the alternatives you mentioned, but much of it is only a guess since I have only done rigid tapping for the past decade.
A tap mounted directly in the spindle requires rigid tapping and a precision machine / motion control. Not an option on a Tormach.
The tension/compression holders seem to be sloppy on the Z-depth, a problem on full thread blind holes.
Reversing heads are huge. Not sure they will work with ATC (correct me if that is wrong), they eat up Z travel, they are not precision depth controlled.
Thread milling is great, but I would be very dubious of counting on it for tiny threads like 2-56 or M2 on a machine like a Tormach. In addition - I prefer form tapping in aluminum instead of cutting.
I have used thread milling for large threads, obscure threads, multi-start threads, external threads, etc....excellent option until the holes are .078" and the thread mill ends up .060" - THAT is tiny and fragile.
My guess is that if rigid tapping was a factory option - lots of people would pay money for it. The design effort is modest. I would certainly pay proper $$ for it.