I suspect it will be further away than a couple of years. I think the current CAN hardware in CPU's can do 1mbps already, but to be honest we aren't going to start speculating or working on something that doesn't yet exist.
It is already on one Cadillac vehicle now....and yes I agree this potentially spells the end as you cannot brute force attack a 5 byte Key unless you have about 10 years to wait, scary thought but the day will come over all platforms when we are essentially locked out for good.