The downside here is the need to proxy everything through the same server. That will add latency and possibly throttle bandwidth if that data is coming from third parties.

The scenario where this could be good is something where there are background jobs running behind the service that would have been API-ed through the same web server anyway.

But I have an ingenious solution for the best of both worlds! An Iframe.

I hear people complain about this a lot. But people who write software that is that efficient are 90-99% wasting their precious time on Earth.

My bad, I finally realized it's better to spend much more time as long as it belongs to other people.

If you go bankrupt before you even get to market, then you aren't wasting any CPU time of anyone else :P