The ban is being proposed for two wheelers with less than 100cc engines which would be manufactured after the ban is implemented. This means, that the two wheelers which have already been sold, can still carry pillion riders.
If you look at the present day scenario, we have a very few two wheelers which are under 100cc and most of them just a few cc lower than 100. The manufacturers would easily do minimal changes to the piston to get them rated over 100cc.
Only vehicle that would need a big change looks like the TVS Scooty Pep with its 88cc engine. As TVS already has many other versions of the Scooty with 110cc engines, they may discontinue the pep.
Overall, with this ban I do not think, there would be any major difference in the two wheeler market, be it in terms of sales or usage.
One thing that seems unclear is the situation of electric scooters. Most electric scooters are rated based on an equivalent cc. Most of the electric scooters come under the 50cc rule and would not be applicable under the MVI act. That is the reason we do not need any driving license or insurance to operate it.
The higher capacity ones , would again be falling under equivalent 100cc category and they would be one of the few vehicles affected by the ban.