The Kawai ES7 seems highly anticipated. Will prices for the MP6 fall as a result?

Doubtful the MP6 is a proper stage board while the ES7 is a portable console DP. Two different markets.
I however can see Kawai coming under pressure to update the MP6/10 earlier then they might have because the ES7 will cannibalize a certain % of sales from the MP6.

Which makes sense. The MP10 is their flagship product but doesn't feature their flagship action, for example. It's totally time for an update on those models.

MP6 is not a direct competitor to the ES - serves a different purpose. However I expect the MP6 will reach a next incarnation somewhere early 2013 (Mp6 II / MP7), with he changes that have been made to the ES right now: RH II / PHI 2

Depends on how long you are willing to wait and what features you need. If you need just a portable AP and good keyed , the ES7 is for you. Only competition I think will come from the new Casio PX350 and upcoming successor to PX3, but no-one has been able to try those yet, since they are not available. Could take a while still...

Note: I expect MP6 prices will only fall when successor is announced. Don't hold your breath...

The MP6 is already very competitively priced...