I have recently come to know that the client libs in AEM 6.4 have been moved out of etc/designs to /apps folder. I would like to know the location under which the project related CSS/JS can be stored or created as a clientlibs folder. Is it okay to retain them in the same location under /etc as earlier versions or should we have them under /apps folder going ahead? This would help us to solve the issue in our project structures going ahead and also to explore the same.
You may check 'We-retail' reference implementation that is available OOB in 6.4
Yes, you may retain clientlibs in /etc/<project_design>/clientlibs for the existing project till you migrate them to /app/<project>/clientlibs
When you plan to migrate, you would need to use proxy configurations - 'allowProxy=true' on the clientlibs to replace /apps/<project> with /etc.clientlibs/<project> and you'd need to allow 'clientlibs' as an extension in dispatcher.any.