Apparently, all of the following are
at risk of changing teirs, because they are mixed up between UU and NU, usually a good indication of the danger zone. I think the UU cut-off is either 3.5%, or 3%, although it does fluctate. However, the UU Teir, similar to OU, is supposed to have around 50-55 pokemon, so anything above 50 may rise, and below may fall into NU.
Into NU:
Charizard Currently stands at 63rd, and 2.75% useage.
Very high chance of dropping.
Typhlosion 54th, and 3.45%, About 50/50 here.
Magmortar 62nd, and 2.87%. High chance of entering NU
Porygon 2 57th, and 3.17%. People have been saying P2 is in the NU drop-zone, so 57 and below is dangerous.
Nidoqueen 60th, 2.99% useage. Quite realistic chance of falling.
Blastoise 51st, 3.67%, at risk, but will probobly stay.
Scyther 52nd, 3.63%, again, at risk, but will probobly stay UU.
Out of NU:
Medicham 53rd, at 3.54%. About 50/50 chances here
Gardevoir 55th, 3.27%. At risk, but will probobly stay.
Hippopotas 61st, 2.96%. Slight risk
Lopunny 58th, 3.09%, Slight Risk
Kangaskan 34th, 6.11%. He's outta here!
Magneton 50th, 3.75%. Has less chance of staying NU than Blastroise has at becoming NU.
Drifblim 49th, 3.83%, say your goodbyes.
Leafeon 48th, 3.84%, say goodbye to Leafeon too, and hello to Earthquake.
Jumpluff 59th, 3.08%, slight risk.
Of course, not all of these would happen at once. If as it stands, Scyther enters NU, then only Kangaskan, Drifitblim, Magneton, and Leafeon would in in danger of leaving, while more or less everything listed would join. If only those as low as Charizard and up in the cut-off, NU will lose a lot more. Hippopotas, Lopunny, Gardevoir, Medicham and Jumpluff will all leave in addittion to the ones that would leave if Scyther was the cut-off.