I'm out of memory? Is the next thing up the Mega644P?

Well, calling it a new name and posting about in the forum would help.
Not sure how else folks come across it.

Call it something else besides mighty1284, just need to tweak a few names in the variant folder & pins_arduino.h, shouldn't take much. Like make it all Mega1284P, and keep Bobuino the same. Can add 164P, 324P, and 644P variants as well.