100 classes is unwieldy, unnecessary, and off-putting; too much information/too many choices. It's also the equivalent of putting a big red warning label on the new PHB: New Players, Keep Out! This could --- let me stress "could"-- only appeal to a small subset of mechanics-focused gamers (already a subset of the overall player base).
I have to ask the OP: is this a joke and did we all just fall for it? (no hard feelings if so...)
It's not a joke. I'm serious.
If I was lead designer of 5E, I would plan the system in a way that it has design space for a hundred classes. Or at least 50. Because that's how far the system will expand in 3-4 years anyway. So you might as well plan for it. However, it's possible, but impractical, to put all 100 classes in the PHB. I'd probably shoot for around 30, and spread the rest in splatbooks and Dragon.
As for newb-friendlyness: Depending on how you design this, it could be
more newbie-friendly rather than less. Since each class is a clearly-defined chunk, you don't need to bake many options into the class itself, at least at first level. As I wrote, once you've settled for your class, you'd make one or two picks from a short list of maybe 5-6 class features. That's it. Write it on your character sheet and play.
Code:
[B]Swashbuckler[/B]
Proficiency with fencing weapons, main-gauche, buckler, light armors
Medium hp
Skill: Savoir Vivre (Cha) +3
Class features (pick 2): Taunt, Chandelier Swing, En Garde,
Riposte, Sword & Cape style, Dashing Swordsman
That's the entire first level. You'd need to read the 6 class abilities, pick 2 and understand the unique class skill, but that's it. Everything else is default from your ability score picks, given to all classes, or irrelevant.
That's what I mean by focused: Everything you could want from that archetype is right under your nose, you don't need to piece together skills, feats and whatnot to get there.
If not, well, let's just say if we run a competition for the worst ideas for D&D Next, this is a strong contender!
A few years ago, allowing humans to multiclass was considered a strong contender for the worst ideas for D&D Next.