I don't know so much about pools and their motivations, but (if I were part of such an operation at present) I would think that if I miss the newest ASICs, probably my competition will go for it and I will be a loser eventually. And because everybody else is thinking the same, I would rather expect new ASICs to be introduced, although, of course, in the long run, it is shooting your own leg.
its more about the ones that are first with ASICS (th manufacturers who the Quality assure test the hardware before delivering in december to customers)
(simply numbers by dividing the millions down to simple digits for simple demo)
imagine the network was at say 56hash (call it 4x of s9 miners 14hash)
instead of swapping 4 s9 for 4 s15(28hash) which would make that pool able to achieve 112hash
they instead swapped 4 s9 for 2 s15 to get 56hash capability.
the costs would go down meaning they can sell for less and make a profit. or even now and again swap 4 s9s for just 1 s15 to bring the hashrate down while still profiting
its like in a 10 second race why push yourself to do it in half the time knowing if you do it in half the time youl be expected to half time it every race. better to just race at 10 seconds. and if you can still win without exerting urself then reduce your speed a lil more. thus win without risking cost to your limbs
because you learned from 5 years ago trying to run as fast as possible left you with a 2 year limp.