A list of add-ons that are not available would be a good idea. At the moment I think your notified of only one plugin missing at a time.
A lot of good ideas. Though all of them are not architecture issues that C2 prevents. However please present them so that they can be examined and take a deigns look to see if there is a block. Sooo
* Collision Group/Layers - no blocks for C3
* Exporting ES Group as a Behaviour and Modular object - requested and the doc supports the idea a MAJOR feature
* ES to Objects. The above suggestion would support this design
* Save/Cloud - no block
* IAP - no block
* Leader board - no block
* Achievements - no block
* Steam integration - can't say. Depends on Steams own API and bindings to Cordova, however - no block from C2/C3
* Spline based system - you can read the thread and note that this is a major reason why C3 needs to exist - no block