We should just add a split method to DataValues.jl that handles this case (that is why the * case works, we have that method defined in DataValues.jl).
The two canonical ways to go from DataValue{T} to T are x[] (assuming x is of type DataValue{T}) or get(x). With get you can also specify a default value that should be returned in case x has no value: get(x, "something").
Before the broadcasting revamp I also had lifting via the . operator working, so in that case you could have just written split.(_.Splits, ','), but I never found the time to reenable that for Julia 1.x… I should probably look into that again.