Yes, there will be action in the new gTLDs but like you said, it will take time, huge time before general users get to know (and trust) the new gTLDs. And No, .com will not loose out to the new gTLDs because .com has a history and present with a proven success and trust (among general users).
Yes, there will be a demand and supply thingy (as we often see), when businesses would settle for a substitute domain extension just because they can not afford the .com extension. But in the end, even startup companies who had launched their businesses with .io or any other domain extension would later prefer to acquire their business domain in .com. And do you know why my friend, because there's more authority in .com.
Apart from that, what I can tell is that .com will be the premier choice for the majority of businesses in the coming years. gTLDs does have a charm of their own, but there's little to that side, at least for couple of years to go.