Hi harsha,

The allow-popups is not allowed in 6.7U3, there is no such implementation, it was added post-factum.
There is no way to enable it, since the implementation is missing.

About the suggestions, can you elaborate more on what is the use-case that you try to accomplish ? 
Most use-cases can be migrated from popups to opening a modal and in most cases this is the best practice. However it depends on the use-case in question.