You get no more claim than the other side does here. Additional classes make up the bulk of 3PP player facing offerings, precisely because there's huge demand.
More fundamentally, the design question of "few classes with lots of options" vs. "lots of classes with fewer options" vs. "multiclassing as chunky point buy" is very much not settled definitively.
Personally, I'd prefer the game go crazy with new class creation and ditch multiclassing, which makes the internal balance problem significantly easier. 4e's sin was thinking resource system was not an important part of class identity, and avoiding the hard design problem multiple resource systems creates. That should be faced head on.