I think the greatest breakthrough in lossless compression would come when the development of compute outpaces storage density. Maximum possible compression (entropy i think?) isn’t impossible per say, but it is computationally impossible with today’s computing resources.
Of course, largely hypothetical now, but I envision a time in the distant future where we produce so much data that we must compress it to its principled minimum.
I do agree that current lossless compression is pretty pressed for further innovation given current resource constraints.