I think any more significant advances in willow size wise for the weight will mean more returns to the manufacturers. You need moisture in a bat to maintain its structural integrity, which is why I think that overaggressive drying is stupid. Unless manufacturers are going to offer only 3 month warranty, I don't think much will change in terms of size to weight ratio in bats, I just don't see how it is possible.
Looking back over the past couple of decades, I think I read that 2lb 5oz was a standard weight - now 2.9 seems to be the standard. That's 10% more mass, which is significant, since it suggests that players are just getting much stronger. At this rate, 2.10-2.11 will probably be the norm in a decade's time. Size to weight ratio won't change much, but I suspect that if we keep getting stronger and think that more volume means more performance, then your special super low density 40mm edge 65mm spine 2.8 bat will be the standard dimensions for a 2.11 standard bat. (Could be rambling a load of rubbish, hard to see what I type on a phone)