It's best that Frontlines does not get a ranked mode, as this would have multiple negative consequences and no gains.

Like someone has already said, it would split up the community more as well as have 72s become non existent.

There's a number of more issues that pop up if they did implement Ranked FL, such as 8 player premades would be even more prevalent, putting all the solo players (like me) off the mode just like how they currently do it at times. All the top ranked FL players in a list would be ones that only queue in a premade since the kill potential is greater in a coordinated unit, leading to more wins. Unless they do away with being able to queue as a premade for it and just randomly assign people to teams, it could be a little more plausible.

There would be more angry competitive people in there who care about their rank a lot just like they do in the Feast.