Don't hold your breath. The R leadership doesn't want to prosecute Holder -- I think because someone would call them "Racist!" and make Boehner cry.
My prediction: Holder will kind-of sort-of comply with the subpoenas at the very last minute, with documents so heavily redacted as to be useless. That will be enough to buy a few more months, then it'll be close enough to the election that Grassley and Issa somehow end up being the bad guys.