There are many inconsistencies with this issue.
From my knowledge it must be enclosed to be legal. But it's still defectable if an officer decides it's defectable.
I doubt it's a problem in most cases when it's enclosed and you're just honest with cops, but if you're defected you have to change it to a stock airbox unless you have an engineer's certif. (which still isn't a guarantee).
I think in real-world circumstances you can manage fine with a pod, but it's always a grey-area.