Where speed and enhanced integration needs to be achieved then the c++ interface part of the Illustrator SDK is probably the best route as we used in the integration of Illustrator into SMART boards

CEP User Interface Development

For Illustrator, CEP is the standard way of providing a user interface and uses web based technologies such as HTML and JavaScript. Event handling can be provided you with the C++ and ExtendScript.  The Adobe Illustrator SDK provides interfaces for both commands and feedback.

Adobe Dialog Manager

This is still mentioned in the Illustrator SDK and should just be ignored at all costs. 

C++ Plugins

Adobe Illustrator is primarily written using a language called C++. The Adobe Illustrator SDK has been the standard way for decades to add functionality to Adobe Illustrator. Where speed is important than this interface is definitely the preferred way of developing extensions to Illustrator. C++ code produces DLLs (dynamic link libraries) on Windows and shared libraries on Mac OSX, which on startup add to the core functionality of Illustrator. 

Platform Dependency

Developers need to use platform dependent development environments depending on whether they are developing the code for Windows or for the Mac.  On Windows, Microsoft Visual Studio is used and on MacOS, Xcode is used.

Platform Compatibility

Most of the code using the Illustrator SDK is compatible across both platforms but there will be some elements which are specific. The code is generally more complex to develop using this interface rather than the scripting interface for ExtendScript and often functionality exposed by the C++ interface is not always available to the scripting interface. However it is possible to use the two in combination either directly or through the CEP interface.

Installation

The main way of installing Extensions and plugins now is using the ZXP format. It is essentially a ZIP file with a fixed format of folders containing the files. If C++ has been used then this is known as a Hybrid Extension and there will usually be a Mac and Windows variants of this binary format plugin if the Extension is intended for both platforms. If the Extension is intended to distributed via Adobe Exchange then this format will allow the installation to take place directly from Exchange. However this does not stop the ZXP file being distributed outside this environment and there are now some third party products that allow this installation to be done such as ZXPInstaller.