Well, of course, if it was practical, someone would've already done that, but I'm still curious.
As you can imagine, I'm an illiterate on the matter of aerodynamics, and even though supersonic propeller blade driven aircraft is not feasible because of the tremendous forces they would suffer, I see it as a somewhat of a "barrier". "What would be possible if this weren't a problem?", so to speak.
Well, I can imagine that putting a ramjet at the tip of a propeller would increase complexity and increase the size of said propeller (so all components could fit in), which would increase the drag, but could allow for more air to be pushed.
The closest thing I could find was "Tip Jet", a type of helicopter that uses combustion at the tip of the blades. One of the various attempts had ramjets at the tips, the "Doblhoff WNF 342", but there isn't much information, and I'm more curious about the applications on turbines (which would be tremendously complex).