Interesting, if a very impracticable idea.
It has me wondering what suspension bushing style 'rubber' mounting of the condrod might have on an engine..?
Just a 'Thought Experiment', assuming the ...'rubber' can handle the force of combustion etc:
Imagine that inner steel sleeve is the small end bearing and the outer steel sleeve is the condrod.
Assuming momentum overcomes 'piston to sleeve' friction; one should get a slightly longer stroke (swept volume) on all but the compression-power, 'stroke ends'.
A higher swept volume is good (for all the usual reasons) and there should be a perceptible increase in engine 'smoothness'..?
For the end of the compression and the beginning of the power stroke:
The rubber should compress some, despite the piston deceleration, thx to the compression pressure.
That means a lower compression ratio, for a higher swept volume.
Then when the pressure 'hits' the piston on the power stroke; the rubber will compress more and later give a bit of the OP's desired push to the crank at a more desirable crank angle..?
A similar 'rubber' thing could be done to the Big End side of the conrod too.
That increases the discussed effect and should reduce shock loads on the bearings.
All in all; a er... 'rubber mounted' conrod may just result in a perceptibly 'smoother', more refined 'feeling', slightly more efficient engine, with longer conrod bearing life and a less shock stressed/fatigued conrods..?
If I were doing my University Thesis on engines; this might be an experiment/subject worth considering!?
(What 'rubber' might withstand the pressures, temperatures and oil and how thick could one make it?)