The Steelers have $700k of cap room. They have no room to sniff anything. TT might make the offer for the simple fact the Steelers can't match it. The Steelers definitely can't offer Shields anything.
sportrac.com shows they have $1.9 mil in cap space. If they fire William Gay (which would be the whole idea in the first place) they'd pick up another $1.2 mil cap space. If they lose McLendon, that's another $1.3 mil in cap savings.
Nothing is etched in stone. But your point is well taken. The Steelers have a ton of dead cap space tied up in their top 15 guys. There's not a lot of room to clear more space without losing a presumptive starter, and it's a bit late to go all Ravens on the roster since the replacement possibilities are getting thin.
Besides, that post was more about making a point about TT rather than the Steelers.