Can you stack voltage regs for higher voltage?
Cascoded (stacked) circuits are not something unheard of. Here is an example from Texas Instruments,



However, to have a stable (elevated) ground for the upper regulator U2, the bottom regulator U1 should be able to source AND sink the current, which is not the case with TPS7A47 nor LM1084.

Good thing is that the ground current for TPS7A47 is no more than 1 mA, so you might want to load the U1 with more than 1 mA extra load, so you will have some regulated output both ways. Obviously you would need proper load capacitance on U1 and U2. 

Obviously the output noise will likely go up 40%, because the noise of U1 will be added. Also you might have overall stability issues, due to modifications to loop transfer function due to extra impedance in ground point. Here is one example when this kind of circuit was not successful.

The concept of "output impedance" is not used in LDO regulator technology, so you would need to look for quality of regulation (ripple rejection, load transient response, etc.) I don't think they will be affected much if the overall circuit will be stable.