Kinda missing the point. There is a step change in the system cost when you move from an all-in-one micro to external memories. So your micro is $5, and your DRAM is $3, and your external flash is $3, and some external bus logic is $1 and your PCB now needs to be six-layer or more to handle fanout of the uBGA packages, and you now have extremely high-speed signals on your PCB (previously confined within the micro), and... and... and... - it all goes hand in hand. You can't just say "micro X is cheap" because by itself, a micro without memories is useless. And, to continue down this line of thought, here's what our Atmel rep explained when I asked him "why can't you make a micro with 8MB of internal flash?": The silicon of a micro is complex (ESPECIALLY these mixed-signal chips we're talking about with radios and ADCs and so forth); they have many layers and process steps and consequently low process yield in terms of defects per square millimeter of die. So, the larger each chip on a wafer, the smaller the percentage of those dice that will be defect-free and saleable. If you just add a massive NOR flash array baked into the side of the artwork, you wind up with a die that's a) low yield because it's made on a process way too exotic for the simple flash array, b) consequently way too expensive. There is a complex break-even point calculated between the price the market will pay for a part with X amount of internal memory vs. die size, yield, the cost of packaging devices that have many pins, the possibility of stacking dice, and doubtless many other factors he didn't tell me about. So that's (part of) why manufacturers only make all-in-one chips up to some flash/RAM size.
In other words: don't expect to see a chip with 32MB flash and 512MB RAM internally any time soon. I'm sure you could put together a *system* that can run Brillo somewhere in the sub $10 BOM cost, but this is an order of magnitude more expensive than one would put in, say, a door sensor contact. So Brillo seems intended for the expensive side of the smart/connected device landscape, or for hub type devices, not cheap ubiquitous sensors.