FWIW, the availability of a 17-4 ph sst frame would be very desirable. The weight of these guns is not the real issue, it's the size that counts. SSt and a barrel capable of +P rounds would be the next new pocket bomb and an important evolution of the arm.
One could speculate that a 45 acp capable gun would have to be steel framed, as necessary to maximize the inertia, durability, accuracy, and feel in the hand. So, a precedent for a SSt 9mm might be there.
About the Stellar holsters, the 'spare mag on board' is what sells it for me.