I think we should see this whole thing as a kind of anti-Ark. In Zechariah 5 we have the following:
- A basket with a lead covering
- Containing a woman identified as "wickedness"
- Carried by women with stork wings
- Carried to Shinar where a house will be built for it.
Contrast this with the Ark of the Covenant:
- An ark with a golden covering
- Containing holy items
- Flanked by golden winged cherubim (1 Kings 6.27)
- Carried to Jerusalem where a house was built for it.
Consider that Zechariah's night visions are very strongly associated with temple language. The four horns of chapter 1 are an anti-altar, followed by the measuring angel in chapter 2, the high priestly garments in chapter 3, the lamp stand in chapter 4, and the chariots in chapter 5 (corresponding, perhaps, to the water chariots in the temple?). Given the multiplicity of allusions, it makes sense to see the stork-women as de-glorified cherubim for an inglorious and wicked anti-ark.