I am at the early stage of development of a big scale RIA that could become a friendly or scary monster based on the early choices made at that early stage. The current prototype has been developed in Flex 3 and around Cairngorm 2. The current prototype is very simple but this application is going to grow and incorporate many more modules, some created in Flash, some other in Flex. The system is will be used by multiple administrators each of them administrating one or multiple workgroups and users that can belong to one or more workgroups.The application also needs to be able to incorporate extra modules like a messaging system, chat rooms and upload-download system. The application will be using web services and send data back and forth to a database.
My current concerns are about scalability. I am aware that there is nothing like a perfect choice in term of framework but which framework, you reckon, would be the safest bet for the 5 years to come ?
Also is it wiser to stick to Flex 3, refactor the code and port to Flex 4 (which seem to me like a transitionnal product at the moment with the mx and spark component) or wait for the next version of Flex ?
Your comments are much appreciated