I'm guessing most of you aren't at the point where trade ships cost 80m each and in order to get my last 90 it will run around 7b in gold so buying more isn't really an option. 500 vs 1000 carrying capacity isn't going to make much of a difference. They could even keep it lower on new servers since resource quantities aren't what they are on well established servers.
My new ship currently costs around 3 million, so i am indeed far off what you are describing. but doubling the capacity would have the same effect as increasing your ship amount by 100% (from 380 max to 760 max).
I also have 16 freighters. for me it is enough for now, but i do have towns close together. i think that they are also quite forgiving when it comes to their gold cost, so getting ~100 of them shouldn't be that difficult especially for larger accounts who need them the most.
Just how many trade ships and freighters do you have exactly? i agree with you that in few years there might be a need to increase the capacity, but i strongly believe that for now freighters can do just fine.
I have 475 trade ships and 105 freighters. The freighters are good enough for my current needs.
With the increase in what players are holding now and needing for upgrades it would make sense to also increase other aspects of the game like trade ship capacity as well or at least lower the cost of trade ships by 50% so it is realistic to max them out.