FPSC and good quality commercial games YES!!! But......
First of all define commercial game. What's your target?
If it is creating the next Unreal, quake or anything along those lines, forget about it. When it comes to gfx it would be possible (but not guaranteed), but when it comes to the programming (or in this case scripting) power, FPSC will fail.
Will combining DBP & FPSC be powerfull enough? I don't know, I seriously doubt it. I've yet to see the release of a top title (again in the same range as the 'big boys') created with DBP.
You may as well face it from the start.... even though a number of these engines claim they can do it (Blitz 3D, 3D GameStudio, DarkBasic Pro, Torque and so on), none has proven it yet. I seriously doubt you can create a top title (which sells for around $50 or around 50 euros in the store) that is presented next to the big game studios.
But not all is lost, I do believe you can create a commercial game with FPSC. But you have to target a different market. Games created with FPSC could very well be aimed at the low budget market ($9.99 or 5-10 euros price range) and with some effort you could even target the mid range market which has been growing over the years (the $19.99-29.99 or 15-30 euros price range).
I've been involved in a number of succesfull low budget game projects that were created with less powerful and gfx wise less stunning then FPSC is.
You can create a great story like, you can create good gfx, but if the game play is bad or very limited, the game will not sell. Some of you do quote some titles of the past, but times have changed. The public is more informed and more demanding these days when it comes to A+ titles. Even larger studios/publishers aren't releasing all of their games as A+ titles anymore. They've got some great games, but there just not good enough. These games fit well in the new mid range market segment and are thriving there. I've even seen some excellent game being released as low budget, they just didn't make it into the other segment and the publishers didn't even try to market it there.
FPSC and good quality commercial games YES!!! But..... don't aim for the top, you'll only get dissapointed. Aim for the low budget or mid range market and you'll be much more succesfull and satisfied in the end. That way you can really achieve something and so not end up dissillusioned or dissapointed.
If I do use FPSC to create a FPS? What's a FPS supposed to be anyway???