I think it's hard to say whether the Kindles will be refreshed. Sales on dedicated ereaders are down from what I've read and the current devices are excellent. I wouldn't be surprised if they're around for a while just as they are.
Of course Amazon might decide that refreshing them generates interest so I could be wrong. The only thing I ever learned about marketing was while selling Fuller Brush door to door back in the early 1960s and I nearly starved.
Barry