You dont even need the free trial for alts if you pay the higher price. I am able to create more than enough alts but managing your inventory through alts is quite annoying. First you have to go through parts of the story again and have to get to 15 (?) or something to even get the retainers. After that you need someone or the FC chest to exchange your items since its not possible to befriend your Alt and thus you cant sent them post.
If you need another person to exchange the items this makes it really not convenient enough. Either because that person is not on when you need the items from your alt or its just way to slow in general. Maybe this could be something for items that you rarely need.
I for example own a personal FC. There is only a rl friend in it and my alt character. To have her in the FC I needed another person that invited me when I was on that alt character. It is a lot easier to exchange items since you can just put those items in the FC chest but its still annoying since you need to write down what the Alt has and you need to relog a lot.
So yes theoretically one could use an alt as storage mules but we should not need to go the extra way just to store all these things. Also glamour items which do take up a lot of my space (one whole retainer for it), housing items from events and other personal items are not exchangeable. So the problem with them still remains.