That's actually how a lot of Kickstarters succeed, is the rewards and stretch goals...
It's also one of the critical factors behind why so many Kickstarter projects are a 6 - 18 months late. No, every rational, reasoned analysis of Kickstarter projects I've read, by outsiders and the Kickstartees themselves, has blamed stretch goals and rewards for both delays and funding problems. It's one thing to over-commit with the project itself, but if you're over-committed on the project you're likely to over-commit on everything else, too, so if there's a problem, all the extras just magnify those problems out of proportion.
Given your existing concerns about his ability to deliver on a timetable, even if he does go full dev mode over a summer, lots of flashy extras are the LAST thing he should be considering adding to a Kickstarter.