As blown gasket states, for the direct route there's
1. High LSALTs with increased 02 demands. Most of the continent is over 10,000' LSALT (it's the highest continent after all)
2. Low atmospheric temps (below -70C) below ~63°S for half the year. Speeding up won't cut it. Descent to <FL300 is required to stop the fuel icing.
3. No runway on the continent would be suitable for an alternate. They are normally not maintained except when there's a flight. And by not maintained, I mean no markings, covered in snow and no-one there. EDTO rules also have a pax care plan after diversion. There's only one place on the continent that could cope with an influx of 200 people at once.
However they appear to be wanting to fly a bit to the north as they want the winds and need to avoid the aforementioned problems. PER -EZE over Tassie and onwards would be broadly similar to the current MEL- SCL with, obviously similar EDTO restrictions. As such, I am not sure that it's a great game changer.
You could just as easily fly SIN-MEL-SCL at 07:25 and ~13:35 sectors. Total 21:00.
SIN-PER-EZE 05:15 Would need to do PER-EZE in less than 15:45.
Here's a 330min EDTO with GS to match scheduled times for MEL-SCL - and it's 15:40!
http://www.gcmap.com/mapui?P=Per-S65...0&SU=kts&E=330
Coming back would admittedly make a difference of a couple of hours.