my take...

The weapon/shield will be replaced by better gears...fairly easily.
The armors are quite subjective to your luck....

Vile ward is an example easily replaced armor in RoS beta.

Percentage based are more difficult.
ie:
Attack speed is difficult to find for stats >8%...so are CC and CD based.
Quad and trifecta items...

Current Gems dropped in vanila is assume to be worthless if the RoS beta gameplay is expected...
New Gem Plans would be required to craft...if you have a group of non-profit friends/clans...they/you might craft for them.

So Gem selling service/crafting is probably something after 2-4 months in the game...

Most people will be scurrying to paragon level.

Good drops are expected in Torment level...depending how fast your build can go there, and MF.

The game will reach saturation point once everyone gets drop in Torment 6.
like now..MP10.

You can't sell items.. you can just keep on crafting and etc...after completely upgrading your paragon to level 800, to max all your stats.

So, you are just going to "Wow" "Wow" like 6-9 months..., and then feel bored again at some point....