I think there are much better ways to implement a time/movement-based ability. As you've said, an inertia based movement with acceleration would lead to problems with quick change of directions. This is a big issue, because one of Bo Jackson's surprisingly good options is the ability to jump and weave in and out of melee range.
I think a good idea that goes along this line would be to have a power meter that charges up as you run in a direction. It would be a binary meter, so as you run to the right, the meter moves towards the right, and vice versa for the left. If you stop it goes back towards 0 faster. This is so you can't just build meter by running back and forth.
Then you can use the meter to do special attacks. Like maybe 25% and you can do a mega tackle, and 50% for an temporary speed and attack boost. This would be better than just a straight up momentum based damage buff, because you have to manage how you build your meter before engaging an enemy.