The "standard sensors in a form factor" sounds nice, allowing a price range of sensors depending on ones needs. And would allow different mounting options (space, interference, cog, etc). But would most likely lead to a board attached to an adapter board for the SBC (more size/weight). Seems worthy of discussion.
The $5 Pi, given it's size/weight, looks attractive. Especially if you don't need quad core processing. It's still a big step up from Pixhawks Cortex-M4F. And lacks dead-weight of an Ethernet jack (seems to be useless on a drone).