This would damage the game in the way it is suggested here in the following way.
Let’s say that by far the most popular NK is possessor. With this system in place, it’d be way more likely to have a possessor in your games, losing an aspect of social deduction and class variety. What would work instead is having the game generate the role list for a given game randomly before taking into account preferences, and afterwards match the preference lists of players to the available roles.
Academically speaking the random serial dictator mechanism would probably be best suited for this as something that is easy to implement, computationally efficient, strategyproof and relatively efficient. Other options are probablity serial or rank efficient mechanisms. However any heuristic solution is probably also satisfactory for ToL. Floofyboy describes one way of implementing random serial dictator.
I support this idea as a whole as it can only add to the game, however it might not change much, if the ToL community largely has homogeneous preferences over classes. If everyone prefers MM for example, the system cannot discriminate who should be assigned MM. If this would be implemented, data analysis can quickly make this visible by simply checking the chosen preference lists of a sample of players for similarities.