As houses get more efficient and floor temps drop, I think there will be more emphasis on putting tubes only where people will appreciate the conducted warmth. For example, I expect that feet never touch 2/3 of a bathroom floor. So you have the option of making the 1/3 warmer without overheating the room.

Excellent point. I'm wondering, though, if our keisters will get unexpectedly chilly if we intentionally hold tubing away from a wall where we know there are going to be sofas in order to concentrate it in walkways.

Until you start looking at separate rooms, heat travels quite well via convection.

Bathrooms are critical (ie, you really want the floor to feel warm) because they so often involve bare feet.

Actually, bare feet touch bathroom floors more than any other room. However, bare feet don't spend as much prolonged time on bathroom floors as in other rooms. This is why the max recommended floor temp for bathrooms (and hallways) is 92F and the max recommended floor temp is only 85F for other rooms. It is the prolonged time that can become a negative comfort factor. Fortunately, hydronic RADIANT floor heating systems don't do much heat conduction/convection, so your concern Jonr is largely mitigated.

No ICF, you normally should place the tube as though the furniture will not be there (i.e., furniture tends to move around). However, the design should treat the area that is covered by furniture or heavy rugs, etc. as being "blocked" so as to correctly align the room heat gain with the room heat loss. The only areas that you don't normally want to place the tube is under bathroom/kitchen cabinets and toilets (i.e., because of the wax ring). You also should consider not placing tube (or at least not too much tube) in food pantries (i.e., as this can lead to premature food spoilage).