Sinclair offers a similar tool. You still have the problem of inconsistent bullet lengths. I suppose you could trim the bullet nose for each bullet you want to set and track seating depth for and use that, but then there is always the issue when they change the ogive profile of the bullet without changing the product number.
As long as your the method with the Stoney Point/Hornady tool is consistent, you'll be able to keep the bullet in the same relative position to the lands as the throat lengthens.
However, I have a 5/16 x 36 tap, and I like your idea of using a fireformed case. I have already gone to using Sinclair tapered steel inserts vs the origial aluminum inserts, and I am using a custom made piece of drill rod vs the plactic rod that comes on the Hornady tool nowadays.
