Back in the olden days of tailfins and rock 'n' roll, car air conditioners and seatbelts were aftermarket accessories.
Anyone who's been using personal computers for a few decades can remember when nearly everything was an add-in or add-on. (Remember Trumpet Winsock, or memory managers like QEMM and 386MAX?)
If Google determines that it can serve users better and secure or improve its market share with features that have the side effect of hurting SEOs and other third-party vendors, it would be foolish for Google to hold back simply to protect the interests of those third-party firms. (Did the car companies hold up progress just to keep manufacturers of carburetors or aftermarket air conditioners in business?)
You'd probably leave Google unless you were just looking for a quick snippet of information, once you found a search result that looked interesting.
In any case, being able to preview search results on the SERP does sound like a pretty compelling and handy feature for users. It also should create opportunities for SEO/SEM consultants who can shift their mindset from "How can I make a search engine think this page is relevant and useful?" to "How can I make searchers see that this page is relevant and useful?"