I haven't checked but there may be a way to transpile Angular 2 into Angular 1.4 (what Kibana lives in). And if such a thing exists, then you would want to alter a build process in your plugin to transpile the Angular 2 into Angular 1.4 THEN run through the typical Kibana build procedures.
The other way would be to create a secondary build procedure within Kibana itself to compile and optimize your Angular 2 plugin separate from Kibana. In the end it's all vanilla JS anyway.
I would recommend just writing the plugin in Angular 1.4, it'll save you a ton of headaches. And in the case of option 2 it'll actually save the size of the plugin (imagine having all of the bloat of Angular 2 just for one plugin).