User blog comment:Nord Ronnoc/Details of new Mass Effect game from private PAX presentation/@comment-4721065-20131126114729/@comment-1679409-20131127161551

The Leviathans seem to be more of a manipulative race that would work through enthrallment (i.e., a milder form of indoctrination). The same was true for the Reapers; they did most of their work through the geth and repurposed creatures like the Collectors and husks. So, the presence of new races does not in and of itself mean that the Leviathans couldn't play a role.

Not saying that it will be them, just pointing that out.