Also an opportunity for "concierge" service -- "Find/replace all instances of api.stackmob.com with api.example.com, and give us your credentials on StackMob. We'll take care of everything else. It's our thanks for signing up for our $500-a-month-until-your-business-dies plan."
Edit: It occurs to me that this is slightly complicated by the need to have API compatibility with StackMob, and I don't know the space well enough to know if anyone does that. In other PaaS businesses I'm aware that some companies maintain drop-in replacements for the market leader, because they make it possible to poach clients without asking for a $X00,000 rewrite.
Sounds more like one should not use this kind of solution unless it's very temporary or one is building a quick prototype. What about businesses that relied on stackmob? welcome to the Baas area.