Two or three years in a row now, both Song and Fabregas pick up stress injuries in the second half of the season due to being overplayed.
Next year, Wilshere quite likely will as well. In fact I wouldn't be surprised if he did next week.
We need at least one new option who will not cost us points in at least 75% of "important" matches so that Wenger can confidently rotate all of Song, Fabregas and Wilshere against almost any opposition. A player that genuinely contends for a place will keep all three of them in better shape physically and mentally.
Unfortunately I don't think squad options like Lansbury would really help out more than Denilson and Diaby. Just like them he will only really be used in the first team after injuries bite or in irrelevant matches.