We already have an effective ASuW capability, it's called the Submarine Service
On a more serious note, the need for a modern + effective SSM for our escorts is very important, too important to just leave it 8 years and invest in an anti-ship missile for the JSF.
After all, carriers
might not always be around when ASuW capabilities are required.
Personally, if a RN carrier battle group was established i would like the FAA to focus on CAP/CAS and only being called in for ASuW when absolutely neccesary rather than people saying "well, we have naff SSMs so can't really do much so divert some JSFs to take out those ships".
What i'm trying to say, ASuW should be a secondary (or even tertiary) role for the JSF - much akin to the FA2 - and let the escorts deal with surface threats unless completely neccesary.