I am 99% sure that Phyrexia is going to invade Kaladesh, with it either happening in the next set, or very clearly setting up the invasion for our return to Kaladesh the next time around
While Sram, Senior Edificer is also good draw, its only off of cast, and so should always be second choice to Puresteel
To put in more specific terms, Im 1/80 to get a Borderless Wrenn and Six of any type, but Im 1/160 to get either a Textured foil or a Borderless
The enter the battlefield trigger on this Sphinx is especially ridiculous in a four-player game as you end up generating mana and card draw every time you cast the Teller of Secrets
Secondly, in decks with a way to sacrifice a lot of cards for value before bringing them back for another go around
Great in all format, and even better in Commander, where your opponent gaining 7 life isn't that big of a deal