Source: Blue Post

The drop chances for Son of Galleon's Saddle, Reins of the Heavenly Onyx Cloud Serpent, Reins of the Cobalt Primordial Direhorn, Reins of the Thundering Cobalt Cloud Serpent, and Solar Spirehawk have been greatly increased.

Is there any consensus on what the new drop rates should be?

Not really consensus, WoWhead has been collecting data though.

• Solar Spikehawk - 36 out of 602 (6%)
• Heavenly Onyx Cloud Serpent - 41 out of 6,113 (.7%)
• Cobalt Primordial Direhorn - 24 out of 3,124 (.8%)
• Thundering Cobalt Cloud Serpent - 31 out of 3,369 (.9%)
• Son of Galleon - 29 out of 3,655 (.9%)

Combined MoP world boss drop rate - 125 of 16261 (.77% or 1/143)

Sounds like 1% might be a reasonable estimate. Not sure about Rukhmar, seems like a statistical outlier due to the small sample.