sounds more like a custom solution that might be achieved using lua + nginx;

from what i understand you have a "static" part that should get send early/from
cache and a "dynamic" part that must wait for the backend?

the only solution i could think of in such an asynchronous delivery
is using nginx + lua, or maybe varnish (iirc you yould mark parts of a
page cacheable, but dont know if you can deliver asynchronously though)



regards,


mex