The general policy is to release code to facilitate your use of Teensy, even for commercial use. I do indeed publish a LOT of code! I want you and your project or product to be successful.
However, the one commercial use that isn't supported is making a direct clone of Teensy. The problem isn't you. It's Sparkfun, Seeed Studios, iTead and numerous other companies whose business model is making and selling "open" hardware with minimal engineering investment. Arduino can survive such cloning (through it's causing them a lot of trouble), but PJRC can not.
Back to your product, which obviously isn't a Teensy clone, you're obviously going to create your own board when/if the volume is high enough. At very low volumes, the most sensible approach is to just solder or plug a Teensy into sockets on whatever you're making. How you run your business is, well, your business, but for anyone reading this, I've seen numerous attempts focus all these energy on minimizing hardware cost rather than building customer relationships and ultimately selling their product. That's not usually a path for success. Rarely does a new product immediately sell in high volume, so a successful approach usually involves trying to make sales first, then optimize for low cost when doing so actually saves real money.
For Teensy 2.0, we started selling a pre-programmed 32u4 chip, to support people making the transition from using a $16 PCB to designing their own. The $8 chip is still relatively expensive (you are buying software, and also a physical product which we handle in low volume), but the pre-programmed chip lets you take the step of making your own PCB without also needing to take the difficult step of transitioning to different software at the same time.
For Teensy 3.0, we'll certainly offer a pre-programmed Mini54 chip at some point. It will be in the larger TQFP package. In fact, I recently purchased the ZIF socket we'll use for programming these chips, but I haven't built the board and a version of the test fixture to program just the chip. There's still a lot of software work to do on 3.0, so this is near the bottom of my priority list... but also it's a low priority because so far nobody has really needed it. I'm sure that will change over the next few months.
Ultimately, if you're selling a product in high volume, you'll want to make your own board without buying anything from PJRC. For Teensy 3.0, you've got every last line of source code for everything on the MK20 chip. This was one of the goals of 3.0... to let you transition from a Teensy board to your own board, without having to program a bootloader onto the MK20 chip. There are companies that make programming hardware meant for using Freescale's chips in high volume. P&E Micro is the main one. You'll probably buy something from them? I can't help you select a P&E Micro product, but I'm sure their sales people will be more than happy to help!
I want to help you with using Teensy to at least get your commercial product started. Really, I do. I there's something you need, just ask me. I'm reasonable. I put an incredible amount of work into Teensy, and ultimately make far less than before I left my professional engineering job, because I really do want to make a platform you can use to be successful.
But please do understand I get a LOT of these questions about transitioning from an idea to a high volume product when they're very early in the idea stage. In fact the contact often happens as a phone call before even buying a single $16 Teensy and trying to physically build a first proof-of-concept prototype (and rarely do those lengthy conversations turn into a single $16 sale). I'm usually happy to help, but Teensy is ultimately about a platform that helps you to help yourself.
Also, keep in mind PJRC's business model is based on much more engineering work than most companies in this market. Honestly, it's not a great way to be profitable.... the "open hardware" money is in distribution of parts and sale of other people's designs, where minimal engineering effort is needed. Even Arduino primarily aggregates 3rd party contributions, though only recently they've finally hired a full time programmer (Christian Maglie) now that they've grown so much. PJRC is not even a tiny fraction of Arduino's size. In the market of Arduino-compatible boards, there is massive cloning. For an example, look at Sparkfun's "Pro Micro" board, which is amazingly similar to Teensy 2.0. The Arduino first announced Leonardo and published beta test code which they clearly said was not ready (and they weren't selling Leonardo boards), Sparkfun took that code, made a PCB from the pinout map, and started selling it with the buggy bootloader. Adafruit did the same, only briefly, but quickly discontinued using the buggy bootloader and offered to replace the boards for people without ISP programmers. Sparkfun kept selling the board and aggressively marketed it on their website, selling many hundreds (at considerably higher price than Teensy 2.0, by the way), even though they were well aware it had problems and their web page at the time specifically said to expect bootloader bugs. Had Teensy 2.0's very stable bootloader code been available, you can be sure Sparkfun would have been selling a Teensy board long ago, and PJRC would probably never have been able to make Teensy 3.0, nor the numerous Arduino contributions and other code I published.
So please understand releasing code to permits cloning is a sensitive issue. I really wish it were possible, but the commercial reality of this market is what it is. I try to do the best I can, and I really do want to help you to make your project a huge success.