A few years back we started hearing rumblings about Lithium Air batteries being the next big thing, but nothing ever came of it.
Performance aside, if the average less informed consumer, professional or otherwise, is standing in the store and has to make a choice between a 40V or 60V OPE tool or an 18V OPE tool, price point and quality being similar, he's going to grab the higher voltage tool 9 out of 10 times. It matters little that peak performance of those tools are pretty much the same, because the vast majority of buyers never look into it that far.
It's easy to forget that we as a community of enthusiastic tool users represent the best informed 1% of tool buyers.
I suspect that, as always, Milwaukee will rely on heavy marketing to stay in the race long enough to wow us with something "better". Despite what they might like us to believe, I can't help but feel Milwaukee was caught off guard by Flexvolt. Maybe not, but I certainly get that feeling.