Islamic Sharia recognizes gold and silver only, but money "paper money" has been added to it in recent years.
Based on that law, if the currency is not covered with gold and silver, it is not recognized, but it is the political decision that controls everything.
So, in short, if Bitcoin is accepted globally, those countries will recognize and deal with it "as paper money."
Bitcoin isn't just nothing like a rock or a pile of sand. Technically, it has many digital computations on its transactions. It is better than the paper money so it should be accepted by Muslims.