It will be quite an interesting battle between x86 and ARM. I could certainly see Intel eventually getting down to the tablet and smart phone levels of power consumption and cost - or at least close - but I can't see them going below that.
The cut off point between "microcontroller-based embedded systems and sensor nodes" and an IOT device will be up for a debate that will influence this market quite a bit. For example, if a device consists of a small 32-bit ARM and a WiFi module, with a total bill of material cost of $15.00, is it too small to be considered IOT.
What if that device is connected to your garage door so you can check status and open and close it remotely? I'd call that an IOT device even though it would quite likely be possible with 8 or 16 bit MCUs.
if x86 only focus only server and high margin, it is going to be another IBM.
Leaving $5-$10 chips on the table is the most dangerous things for x86.
MIPS and PowerPC will not penetrate unless management drastically come up with some real value...