I think there is something to be gained in staying in juniors if they don't win jr worlds, as there would be a pretty easy path for them to do so next season (assuming both P/V and L/L move up, I'm not sure on the ages of either couple and whether or not they must do so), I find L/D quite unimpressive, and could actually see their young compatriots C/P being their main competition.
Popova/Vlasenko will move to seniors next season (100%), and will drown in Russian field. Loboda/Drozd are the youngest out of these teams, they actually planned to stay juniors for two more seasons, since he's 19 and she's only 15, I'm not sure if something changed in their mind to this moment.