think about it if you were a miner, and have learnt that you can charge XXX for transaction why would you be happy to again charge just one X?
It is certain the more popular coins will increase costs to catch up with bitcoin, as opposed to bitcoin lowering .
Developers are already being pressured to behave in ways that I dare not repeat.
I dont think that bitcoin transaction fee could ever be come down because there is no proper regulating body over body and people there are just doing according to their will there is no such authentic regulating body who could keep over all these activities and should take care of the consumer rights that in any way they should not be exploited and if bitcoin will centralised world wide then also the transaction fee will be high because then government will implement tax over the transaction fee but in that case conditions will be good.