A spell (beyond your Priority allocation) during character generation costs 5 karma; a Power Point costs 5 Karma. I would likely allow (or request) that a single spell slot be allowed to substitute for a Power Point.
The problem with this system comes into effect after character creation. A player can easily replace that lost spell slot for 5 karma after character generation. They cannot buy a power point after character generation. This means that someone could easily sacrifice 6 spell slots for 6 power points, spending 0 karma at character creation, and then spending 30 karma later to replace those spell slots. It is, in effect, allowing a player to buy power points after character creation.
Thus, the argument by many is that if you allow spells to be traded for power points, why not just allow power points to be bought after character creation? My argument is that mystic adepts could
never have 6 power points and 6 Magic points, so why should people complain if it costs a bit more to actually be able to achieve that desired goal? As I type this, my two week old daughter is doing the same thing. She cries when she's on her back because she wants to be on her side, but then she cries on her side because she's not on her back.