>2. Should an API be considered eligible for copyright, wouldn't that enable opportunities for language and library developers to restrict others from developing competing (via performance or utility enhancements) languages/libraries by forcing anyone who wished to implement enhancements to either purchase a license or flat out deny them the ability to do so (assuming the product --including the API isn't open source)?

It would be a software patent except not by name and it would last significantly longer. I can already see both software and hardware patents being abandoned if this court sets a precedent that APIs can be copyrighted. The next day people will want to add everything patents do simply because copyright has a longer duration and it is effective immediately.