It's been tried. But no real advantage and a lot of unnecessary work.
Cast bullets swage to bore diameter as soon as they enter the rifling. Lead is a dead metal, and it has no elastic spring back, so once it is squeezed down to bore diameter, there is very little shear resistance.
Jacketed bullets are coated with gilding metal and remain tight all the way up the barrel. That's partly why they can be 0.003" smaller than cast, their elasticity keeps them firmly against the lands. Moly lube helps (at least in theory) lube the gilding metal and keeps the copper from abrading off.
On the other hand, leading is thought to be from propellant gas leaking around the base of the cast bullet and taking lead with it. That lead is then deposited on the barrel. It's a different mechanism unrelated to friction.
These photos may help. They show jacketed bullets, both coated with moly and uncoated, after passing through the same rifle barrel. The bullets were not fired, but were hydraulically driven, so as not to risk deformation by the target. The moly coated bullets are purported to show less deformation to the driving area, and smoothly impressed, rather than engraved rifling.
Copied from Precision Shooting, Moly-Coated Bullet Drop Mystery Solved, Dan Hackett, Jan 1997.
The smoother profiles of the moly treated bullets were used as an illustration to explain several reported advantages (at that time) of moly coated bullet ballistics. Those advantages were reported to include improved accuracy, superior ballistic coefficient compared to the same bullet uncoated, faster downrange velocity, minimal copper barrel fouling, and longer barrel life. There may be one or two more that I cannot remember.
Practically, these advantages are most useful to target shooter, bench rest shooters, and long range varmint shooters who drive their bullets faster than 3400 fps. Unless the rifle and the shooter are capable of shooting wee, small groups--say less than 0.5 inch at 100 yards--the shooter is not likely to notice an improvement in accuracy. Advantages to Marlin lever rifle shooters would be minimal. Again, moly coating is not useful for cast bullets.