NVIDIA is supposed to release Volta based consumer grade GPUs this year, no one knows when.
These will cost around 10% more and be 30-40% faster while consuming 60-70% the power that current cards do.
They can come to market in a month, or in 6, there's no way of knowing when.
As for them being obsolete, they'll be less profitable than newer cards but they'll still be profitable. GTX 960 is still profitable. THere's a good chance that by the time new cards are out, you'd be close to your break even point.