You can launch on anything if your SEO skills are good. The fact is that if you launch on an alternate extension you'll leak free traffic to the .com owner so your development benefits them as well. So maybe a cheaper way to launch but if anything serious they usually come back and buy the .com as well once the cash flow improves.
If we're at a barbecue and I yell to ya check out skankwhoreslovedacock are you gonna go home and type in .xxx? The answer is no you will type in .com when extension isn't mentioned and it's gonna be that way until I'm dead. Things are changing blah blah blah=pipe dream from people invested in shit extensions or that missed the .com bus. What could happen 50-100 years down the road doesn't concern me as I'll be cremated by then. Invest in winners not lottery tickets.
14-15 years buying, selling and brokering domains and 99.9% of any requests I've ever received from end users have all been for .com domains. End users also don't give a shit about traffic stats, they'll drop thousands strictly based on the domain.