Beyonce will smash; 3 top 10 singles (including a #1 after the SuperBowl performance), the album will open with around 400K and become one of the best selling albums of the year. However it will not be as critically acclaimed as 4 but she still earns a shitload of Grammy noms.
Lady Gaga will do better singles wise; the lead single breaks multiple records. However her albums sales won't top Born This Way's. She will also tone down her image to be more appealing. She will be engaged to Taylor and take a real break after the ARTPOP tour to settle down. (

) Finally win a Grammy for Album of the Year with Tony Bennett.
Katy Perry will have another string of smash hits but the era generally won't live up to Teenage Dream, however she will have more respect from critics.
Rihanna will release another album in November 2013, the lead single doing well as usual. There will be a huge relationship scandal with Chris Brown.
Taylor Swift's IKYWT will go #1, Red on track to sell at least 4M and she will also have the top tour of the year. She's likely to break up with Harry before Valentine and date an older musician, hopefully a stable relationship this time.
Britney will get married and release an album late 2013 but there won't be much promo because she will be pregnant again.
Nicki will go back to her old sound but it will be difficult for her to regain people's respect.
Adele will release an album late 2013 and blow everyone out of the water.
Ke$ha will have another or two top 10 but other than that nothing major's happening for her.