I mean, really, what else is to be improved upon when cramming drivers into a cubic centimeter?
About 8 years ago, ER4 and E4 and Super Fi Pro were the best we could get. Then came SE530 and TFPro which were clearly upgrades. Then 2 years later came W3 and then UM3X, SM3, GR8, CK10, X10, etc but I feel we have reached a plateau here. Now GR10, W4.....I just don't feel these are improving on any IEM's released in the last 3-4 years. Funny thing is, 98% of the general public has NO CLUE how good these IEM's even sound. Yet us audiophiles still seek improvements in some sense.
When you take an amped ER4S, a W3/W4 and a UM3X and what you get from these, where else are we looking to feasibly improve?