A post to this mailing list is essentially the same as asking us since we monitor the forums pretty closely :->
A development SDK certainly does exist, and we make it available to known plugin vendors without charge. Anyone who can demonstrate basic C or C++ competence is eligible to apply for one by sending an e-mail to sdk@eyeonline.com.
Include your full name, mailing address, and email address in the email. Also mention your software development and graphics experience - not like a resume, just enough so we understand what level you are at. A basic description of the plugin or plugins you intend to write is also encouraged.
It helps tremendously if you actually own a copy of the software, or if you are a known proven plugin vendor. Otherwise, provide me with a fairly complete description of what you have in mind when you apply for the sdk, to get me sufficiently interested to provide you with development software.
I will approve your request, and send you a Vendor ID to use with your plugins as well as a copy of the SDK.
Thanks