I'm not sure if anyone else already reported this, but I applied for the Explorer card about 2.5 months ago and got the 30k bonus (because I needed the miles ASAP, I decided not to wait for the improved offer). Last week, I emailed Chase asking if they would up my bonus to 50k, and they agreed.

The miles haven't shown up in my account yet, but I have no reason to think that they won't.