I will take a more centerline approach to this discussion.
I remember a few years ago when our community did away with the national security studies seats at NPS. At the time, the prevailing argument was we needed more seats in technical degrees and less in non-technical degrees because the idea of the IDC (now IWC) is we would lean on the strengths of the other communities rather than educate and train some officers broadly.
While perhaps not exactly the same, cross detailing at lower and lower ranks, in a way, flies in the face of the above argument. Both methods would give some exposure to alternative approaches to problem solving and the strengths/weaknesses of our IWC brethren, but in slightly different ways.
Frankly, I like the idea of opening up some cross detailing opportunities. I have to agree with Yoshi that the XO job lends itself well to getting some exposure to at least one of the other IWC specialties, but 20yearman has a point that the bang for the buck of doing so is still to be determined. Would a person with that cross detailing, broad experience be a better fit for a job like the new O-6 IWCs? On paper I would say yes. We all have a cognitive bias to want to stick to things we're familiar/comfortable with. I see it all the time coming from Navy J39/N39's who love to talk EW, CYBER and STO, but will shy away from the other IRCs because we often don't get much exposure to them. This kind of cross detailing experience lets you sit at a command that is probably closer to the operational level, so you have the benefit of seeing the work from that perspective (rather than from a strategic, CCMD level), and you get to broaden your understanding of what the other IWC orgs can bring to the fight.