Sure, you can make arbitrary restrictions for how to distribute a work in a license. The question at hand is whether you can impose these restrictions in the v

Sure, you can make arbitrary restrictions for how to distribute a work in a license. The question at hand is whether you can impose these restrictions in the viral fashion of the GPL, e.g., on code I write that merely makes use of your APIs. The way that the GPL attempts to enforce this is with copyright law, by not granting you the right to redistribute GPLed software unless you comply with it. By design, it doesn't restrict anything else about how you use the software.