Funny that the search area was defined so far south today. Yesterday after posting the Indian Ocean sectors at
High-res visible sectors for Southeast Indian Ocean - 8 March 2014 - Weather Graphics I received a PM from a user named Chicklets. He has 0 posts to his name and is unable to get past the moderation, but he said this: "Southwest Region, 0100 UTC, four squares over and three down from top left. In the top middle/left of the square there appears to be a nice straight line."
Maybe my eyes at age 45 are already getting too weary to see it, but perhaps one of you can make it out. If it's there, that would place the coordinates at roughly near 43N 87W (within 2 deg), which is right in the area VH-XXX posted. If this artifact is really there, anything going south would easily peg it as MAS370. If you all do crosscheck and identify anything conclusive I will check the imagery and get an exact lat/long set.
I had shunned these images giving any useful information since much of the air mass is subsident, but looking at the images in those southern sectors I do see cirriform clouds south of 40N consistent with jet stream westerlies and heightened relative humidity in the upper troposphere. If the plane got that far south and was at FL450 for any extended duration it would certainly have been laying down a persistent contrail (or a shadow, as that area looks mostly cloud-covered).
I do realize at this point we're grabbing at straws, so this could just as very well be some anomaly in the cloud texture.
Regarding the mention of 250m AQUA/TERRA satellites... that would certainly be my first "go to" solution if the flights were in the air during the late morning, but by the time those satellites were overheard I'd expect any contrails to be long gone or diffused into a cirrus layer with an unidentifiable origin.