HP has already included the Web UI modules for Defects and Requirements modules in QC/ALM 12, then in 12.2 introduced a Site Parameter to enable the ''technical preview'' of the test modules.
When 12.50 came out, they announced they would ''temporarily'' stop supporting the Web UI modules.
From the 12.50 What's New doc (http://alm-help.saas.hpe.com/en/12.53/online_help/Content/What_New/wn_alm_1250.htm):
''Web Client is targeted for release as part of our next major release cycle. If you are using the 12.00, 12.01, 12.20, or 12.21 Web Client you will need to remain on those versions in order to keep working with the Web Client, as it is not available for version 12.50.''
In QC/ALM 12.53 What's New document (http://alm-help.saas.hpe.com/en/12.53/online_help/Content/What_New/wn_alm_latest.htm), it still does not mention Web UI coming back.
Perhaps Web UI will come back in the next MAJOR release.