remember that 20%diff is a bit overkill to estimate, because the diff will not grow indefinitely, it will slow down at some point if the price remain there or if the efficiency do not come in
I would agree it's slowing down some. Price has risen a little but not to the level of how fast difficulty is. I think it will slow down a little until more get next gen gear... then I predict fast paced again.
So really hard to tell long term, and there is ofcourse having eventually.
S7 and S5 prices continues to go down in hashnest market despite btc being on a low side as well. Current ROI is quite high but still people are selling their hashes trying to get out of cloud mining due to the difficulty increases.