The new game editior Construct 3 will start in beta in April 2017.
Then Scirra will provide the new SDK.
For addon developers
Construct 3’s addon format is generally similar to Construct 2’s. However third-party plugins and behaviors will need to have their editor script (edittime.js) rewritten in to a new format for Construct 3. This basically involves rewriting the action, condition and expression (ACE) tables in to a new format, and moving UI strings to a separate language file to facilitate translation. However the runtime script (runtime.js) should continue work unmodified. There are a small number of runtime features that have changed in Construct 3, but these are usually trivial to update. We’ll provide documentation and assistance on the forum around this. We’re aiming to have initial documentation on addons ready as early on during the public beta as possible so addon developers can get a head start on porting. Overall it ought to be a quick job to port Construct 2 plugins to Construct 3.
We’re aware some third-party developers sell their addons and might not want them bundled with projects. We will provide a way for addons to opt-out of bundling so they stay in the editor only.