I imagine it'll be on PC, PS4, XB1, and Switch.
I don't see next gen, while a lot of rumors and leaks are going around, next gen consoles are not even officially announced yet. Maybe Mudrunner 3 in 3-4 years time, but I don't think Mudrunner 2 is going next gen.
I agree with @justinlynch3
Mudrunner is already released to all current major console platforms. With next gen not expected before 2020, I can't see how Focus would be developing to an unknown platform and specification and what you would even expect them to deliver.
The only console 'refresh' of late was the Xbox X which is a ramped up 4K capable XB1. With 4K resolutions at 3840 x 2160 or 4096 x 2160, I assume this isn't a reach on a high end PC these days or to most in the very near future so I suspect Focus will build that in. The vast majority of players still aren't on 4k TVs or monitors, so even 1080P visuals with a few nice effects would still look great.
Manufacturers must still keep the cost in an affordable range and graphics costs are still high due to crypto currency mining demand. I'm personally not expecting any huge surprise from next gen specs in 2020. I suspect the key target will be 4-8K + VR/AR support and the architecture around delivering this at the necessary quality and frame rate for 2020 + five or so years future proofing. That alone will likely push the bill of materials cost to the maximum. SSD will probably figure (Sony imply as much) but considering the price point and the inevitable growth in game memory footprint, I would imagine it will be used intelligently, much as a cache to reduce load times and performance rather than replace storage completely. I wouldn't expect HDD to be gone just yet unless you only want to save one or two games on your console at a time. But let's see. A year is a long time in tech.