This has been done in order to make a Diesel Wankel (a Mercedes prototype engine, IIRC), since there's a fundamental upper limit on the compression ratio of a W

This has been done in order to make a Diesel Wankel (a Mercedes prototype engine, IIRC), since there's a fundamental upper limit on the compression ratio of a Wankel rotor, which isn't high enough for a reasonably running Diesel. Though, the "compression rotor" and "expansion rotor" were the same rotor. A pair of ports allowed the lower pressure rotor to empty itself at peak compression into the intake of the higher pressure rotor. The higher pressure rotor exhausted itself into that same high-compression space of the low pressure rotor for a second expansion. Note that the original Wankel rotor invention was a supercharger for a piston engine, so it's use in staged compression was thought of from the beginning.