Takeda is doing more than DNA testing in its investigation. This is from a peginesatide report I found on the internet: "[Takeda] is initiating several lines of investigation in order to identify the root case of these reactions. These include manufacturing/quality, epidemiological, non-clinical and clinical approaches. The investigation is ongoing."
DNA testing is not uniform and, depending upon its depth, scope, and sample size, there is a range of times. The same is true with respect to the other aspects of Takeda's root cause investigation. We just do not know how long it will take.
Another aspect is that both Takeda and AFFY will be facing products liability claims. The statute of limitations on these claims could be as little as 2 years or as long as 4 years. Besides hopefully being able to remarket O, Takeda will want to do a root cause investigation to defend against plaintiffs' products liability claims.