IIRC The SQ non stop to New York initially had a business and low density economy class configuration which changed to all business. Low density economy may have been due to payload restrictions rather than passenger comfort.
A QF B787 PER-SIN-LHR may be a better proposition as this would still give a direct service though not non stop, and would allow a mini hub in Singapore for connections from other Australian cities and the Jetstar Asia network.
Some passengers would prefer a transit through Singapore rather than Dubai and they would be catered for whilst limited seating on the B787 wouldn't encroach on the tie up with Emirates too much.
Time will tell if the numbers workout. Sydney - London non stop in reasonable comfort at a reasonable price would be the ultimate goal.