The cylinders in our ROTAX engines are now done with nikasil, and seem porous to me too. A friend of mine is a Mercedes mechanic, and says the cylinders are simply honed to fit the piston. This may sound normal, but there are no sleeves or coatings, just the block is a VERY high silicon content casting, and the aluminum is removed, leaving the silicon for the pistons and rings to ride on.
I am familiar with Eurotech nikasil service, but have yet to see a sample of his work(or hear a complaint).