There is really not enough information to be sure of anything at this point. Particle along with the Elites on community.particle.io are not revealing anything substantial.
Since we know the main processor is changing, it is a good bet that the peripherals will also be changing. We can always look into the datasheet for the new main processor to see if CAN is supported or not; even then we would not know if Particle would bring the interface out and make it accessible.
There are always solutions, but not necessarily a solution that fits every use case.
For example, you could have a Carloop attached to a Photon, which then communicates over SPI/I2C/Serial to the Boron.
By the way, depending on your location in the world, 4G/LTE might not be an option anyway.
The Boron works on NB-IoT and Cat-M1, which is not quite the 'regular' 4G used by cell phones.
For me in Canada, I have to stick with 3G.
More information here: