I love the idea, though 4 pre-gen characters seems kind of low. It's not like it costs much to make characters... why not toss in ten or twenty, each with a different flavor.
It'll only help new players to find a character that 'fits' for them and that way get a closer bond to the character and, through it, the game itself. With only different 4 chars, there's the risk of choosing last and ending up playing some character you really don't like, which can just ruin the game for you before it even starts.
it'd also increases the re-playability. I understand the whole point is that after playing and liking this, they should buy the real game and books. But some people might want to try it more than once before making that decision but may get bored playing the same thing again.
And, of course, group with 5 or 6 players aren't exactly unheard of.
Edit/addendum: Maybe just a download link where some more free pre-gens can be found wouldn't be a bad idea.
And also, I hope these are built much better than the SR4A sample-characters. I'm not saying they should be optimized builds, but they should at least be somewhat decent in what they're supposed to do.