Mixed-Signal modular system grounding scheme
If you trash your sensors, by having PowerSupply trash use the sensor-to-ground path --- ohmic or displacement currents(capacitive) --- then you'll have a 10 bit system.

How bad can this be?

Suppose your SwitchingRegulator has 100pF of capacitance between Line and Output, with 200 volt/200nanosecond edges across that 100pF. The current needing a return path --- and all possible return paths will be explored thru all your sensors --- is 

I = C * dV/dT = 100pF * 200v/200nS = 1e-10 * 1e+9 = 0.1 amp

And the driving force is that 200 volts.

Do you wanna bet you can achieve 24 bits, with 0.1 amp exploring all possible stray parasitic paths?

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Suppose one of the sensors is a strain gauge, 200 ohm resistance, glued onto a machine axle with 10pF sensor-shaft/gnd capacitance. What trash-floor can you expect?