The main change would be to the power supply, as the esp8266 has a far higher (~300mA) peak current than the ATTiny814 used (~3mA).
Currently, an LDO provides 3.3V from the 24-35V motor supply.
This would need to be changed to a buck DC/DC regulator, as a larger LDO at this voltage would need too big a heatsink for the case.
You should be just fine with a cheap lm1117 and no heatsink, that's what most people use with esp's. Also that's peak current from the radio, which for IOT things is generally very short.
as you note with your edit, most usages aren't going to be dropping from >24V.
> Also that's peak current from the radio, which for IOT things is generally very short.
this is the interesting bit, though.
if you're releasing an open source board design, to have customizable firmware dropped on to it, what do you really know about the radio usage when you're designing the circuit/board?
safest is to spec it for maximum draw on any controller/radio. write the BOM to call for one of the three-terminal drop-in switching regulators ($5), and if somebody knows what they're doing they can put in the original linear part and save $4.50.
