OK so this is entirely speculative and can be taken with a pinch of salt, but....

If the fluff for Militarum Tempestus is that these guys are as solid and determined as they come.... They are subjected to years and years of psychological conditioning, are constantly assessed, intimidated, conditioned to be essentially unwavering and they get Ld drop to 7 for regular Scion troopers....

If the rules match the fluff then can we expect a drop in the Ld of regular IG units?