Developers will take a wait and see approach but if even 20% of RIM's 78 million users upgrade to BB10 they will have a larger market share than Windows Phone. Once BB10 gets 2-3 million users the Apps will come (and quickly).
The other developer issue has already been solved. Fixed the SDK and tools to make Apps, fixed the process to create and publish Apps. RIM's done great work here and are second only to Apple for helping developers make money, I mean I doubt they all just make mobile Apps as hobby. Not to mention the $10k incentive if your App doesn't sell you STILL get paid. Who else provides that?
If BB10 is solid and from a hardware / OS side it's sounding promising, App developers would be foolish to get in on the ground floor if this takes off to any degree. Apple's store is over crowded, Android makes zero money as most Apps are pirated. Windows Phone is doing nothing.