Interesting thread. Couple of thiings:
- there is nothing new that pollen provide important nutrition to the bees. Even human use the pollen for exactly the same reason.
- I do not think, that any substitute may actually substitute the real stuff. If I remember properly, pollen substitute is made mostly from corn "meat", yeasts and may be a few percent of real pollen...
- honey and pollen complement each other.
- feeding keep bees inside, it could limit their ability to harvest pollen.