Well, this system is very simple and the TERA used, and Wildstar use.

Create a item when its use ingame give you 30 days, this item can be bought on the site and come to you via mail and you can sell on the marketplace, give to someone or use.

Will have the Entry and Standard version of the item. The existence of this itens will affect these things:

1º Players who can't pay the sub for a while. (SE will keep this player active on the game and earning money beause someone will pay for that 30days anyway).
2º Some players can think the economy can be affected, yes, but will broke the gillsellers too, because ppl BUY gil on the gilsellers. If they didn't they would not be in the chat all day.
3º The player base will grow up.
and a some another changes.

The fact is: These itens will heal more than any other thing.

Ty.