I don't really know if it's possible to "unify" the series. We've had multiple canon explanations for what happened to the parents, at this point, plus 14 yr old Lara being the acolyte of Dr. Von Croy, which seems harder to make make sense in a complete universe, now.
I think they must have meant unify it thematically, which they did a decent job with Shadow of the Tomb Raider in that department & parts of Rise of the Tomb Raider were like that, with the tombs & traps. Either that, or we're now saying that all Tomb Raider adventures are technically canon, but not 100% the way they've been presented to us already. Of course, some of the canon came from the instruction manuals, not the games themselves, so... I don't know. This seems like a logistical nightmare. Looking forward to it, though.