Particle(.io) looks like a promising platform. I've only used their devices and platform for some hobby projects and one small paid-for project. I like that it takes care of most of the hard stuff for you, which would be good for people who are wanting to build IoT businesses. This may help their success.
C and C++ is the dominant language for embedded devices. As of now, most developer use C/C++. Once the industry becomes a little bit mature(preprogrammed devices are available and affordable), people will most likely switch to easy languages like golang.