I see that there is a driver for Sentinel-1 manifest.safe and I tested it against the tough case of the SLC (complex).
These products consists of three HH-HV dual-pol images, they only overlap at the edges (see screen shot, when I load the *.tiff one by one in OpenEV viewer)
However when I load the manifest.safe, GDAL recognizes that it is Sentinel-1 but its georeferencing is wrong. Three images are overlapped almost 100%.
When I run the 'gdalinfo' the GCPs are only taken from the 3rd image (s1a-iw3-slc-vh-########-003.tiff).
Also the new RCM is going to have the 'manifest.safe' file too. There could be a conflict, if file name 'manifest.safe' is used to identify the sensors.