Quite a few people have tried over the years, the same problems kept coming up though - airguns lack the power / pressure to properly engage the solid sides of the slug with the barrel rifling. Attempts have been made to make a "bore rider" type, where the body of the pellet rides inside the minor barrel diameter and a tiny "lip" at the back of the pellet engages the rifling. The problem with that is that different barrels are different sizes, and some have chokes at the muzzle. When you consider how even standard design pellets like JSB have varying results at 4.51, 4.52, 4.53mm you can imagine how difficult matching a slug to a barrel will be.
Hugh Earl at Pax guns got around the problem to an extent by designing his Piledriver slugs with ribs down the side that were able to deform into the rifling, but these were only successful in long, heavy types and for best results needed a special loading probe that held the slug central as it was loaded into the barrel. In the right rifle they were accurate, in the wrong rifle they weren't.
ps/ I hope I won't get banned for mentioning Hughs pellets, it's relevant to the thread.