don't know much about Linux licences, but being
based on slackware, could it be released as closed
source - commercial? I guess not
Sure it can. I don't understand why people find this so hard to understand.
directly from the GPL-
These requirements [redistribution under the GPL] apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
You can release a product FOR a GPL'd product under any license you like. The only restriction is that if you make any modifications to files protected under the GPL (kernel, other distro files, etc.) you must release THOSE FILES under the GPL when you release your product. (And even this rule has some exceptions - nVidia video drivers come to mind. They modify a section of kernel, yet do not need to be source-available)
Anything you code outside those GPL files you are free to distribute under any license you like, as YOU are the copyright holder on them.
So, in worst case scenerio, this would require you to make your GPL-protected changes available free, under an "emulation enhancement package". That package could then provide a clean interface to your (seperate, commercial) emulator, which you can distribute under any license you choose.
Some Linux "purists" (read trolls) may not be happy... But ultimately, it's up to the programmer to decide if he wants to be philanthropic, or if he needs to gain some profits. The GPL does NOT stand in the way of this.
