It depends how you define "mass" in "mass production". If you're talking hundreds, the Pi is probably a good choice. If you're talking thousands, there might be "better" solutions available through OEM. "Better" as in price, availability, quantity, security and specific functionality.
- Price - $30 dollar a pop might not be much for a couple of devices, but on larger scale it adds up quickly. On top of that, casings and external circuitry can cost a lot of extra.
- Availability - Raspberry doesn't promise to deliver a certain version for any time. They can introduce a new model tomorrow and cease production for the model your application is based on.
- Quantity - Is Raspberry capable of delivering the needed amount of boards now and in the future?
- Security - With its removable disk and open community support it's (more) prone for hacking
- Specific functionality - The Pi is designed to be versatile. LAN/USB/camera/screen connectors, etc. You're paying for all these extras whether you're using them or not. On the other hand, chances are high that you'll need external circuitry to do exactly what you want to do. OEMs can build boards and casings to your exact wishes and specifications.
It's important to know that the OEM landscape has changed a lot since the last 10 years. The abundance of off-the-shelve SoC's and reference designs - and small firms manufacturing Android phones, television STB's and the likes - has dramatically lowered the thresholds for getting your own device manufactured.
While the OEM will give you all technical support they can, you're mainly on your own to implement it. You'll need to have a team of people knowing what they're doing.
So if you have the need and budget - and are not afraid to get your hands dirty - OEM might be a way to go.
On the other hand, the Pi does have the benefit of being a mature product and comes free with a large and very supportive community, including but not limited to this very forum.