The gateway is done away with in V7.2. Need to leverage reverse proxy server to fix same origin policy issue. The gadget configuration that was done through gateway servlet to some extent is built within case designer. However it is limited in functionality and will be expanded in future releases. I am told that in 7.2.1, even the reverse proxy server configuration would not be required and a configuration option would be provided within designer studio to address same origin policy. We are currently in the process of configuring Pega web mashup with parent website using IIS server in v7.2 using reverse proxy server. Will keep team posted once that is completed.
Below is the link for reverse proxy server configuration