Well, nested lists/sub items are supported but you have the following options:
1) Create items that have a unique tag and search for that tag. That will give you a list of just the items with that tag.
2) Number the items, and create dates far in the future for all apart from the first one, and then order by name. This gives you the items in order.
3) Wait for full support from RTM. This is such a largely requested item that support for it must be high on their list. It is not a light undertaking so there could be a wait while they get the back end ready to support it.

None besides tag workarounds at the moment. It's been requested a lot. Sub-list, nested list, dependent tasks, etc.

I use smarlists with tags combined. still working on implementing it most usefully.

thanks