My understanding is the 2017 will charge off a rapid charger, it just will not charge at the full rate a rapid charger is capable of without the updated FW. In the CAN communication between the bike and the charger, the bike asks for a certain amount of charge current. If the amount of current requested is less than the amount the charger is capable of supplying, the charger will only give what is requested. My 2018 EX (027), with pre fast charger FW, charged fine from a fast charger at the 24 hours of starvation ridge race so I would think a 2017 MX would also charge from a fast charger. It just wouldn't charge as fast as it would if the FW was updated.
