Could there come a limit to the G-cycle? Like either a) marginal gains slow/stall progress or b) more connectivity simply not being better? Curious to hear from folks in this field if this question has been raised.

Not soon there won't be.

There is no reason you can't have phased array antennas of tens of elements on the handset and thousands on the masts, to give a massive bandwidth increase.

It will take a lot of generations to get to the limit physics sets.