CloudRecognition based application

I am trying to build a cloud recognition based application using unity3d editor, I'll have some targets and metadata saved in cloud database, and some trackable 3d models that will be saved in seperate server, while using this application users will make some extra  interaction by uploading their own models, and render this 3d models with already defined targets that are stored in cloud database. As i said while using unity i can use assetBundles to load 3d models from server.

Is there any way to include new 3d  models  that were downloaded by users to AssetBundle, or do  we have any 3d model converter that will  make AssetBundle

format

Or can you give me any kind of idea to make such kind of system