This will usually transpose into a Modern Exchange Variation with 7...c5 8.Nf3, it's not a bad move at all.
It is true that 7.Nf3 leaves some more options open, but if you want to play the variation with Rb1 anyway I see no problem with it.
Grunfeld 7.Rb1!?
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Recently I encountered this system against the grunfeld:
Is this move not played because it shows white's cards too soon, or does it actually have a defect? I didn't know, and tried to return to civilization with 7...c5