As for an estimate the best we have comes from the second most recent Kickstarter update,
"Some have asked for an estimated release. But since we have definitely not hit our milestones in the past, we are now hesitant to make more promises that we may not be able to keep. But if we were to make some very rough, conservative goals, our hope would be the following:
• New builds on Humble by this spring (April/May)
• Backer access to the game on Steam this summer
• Steam Early Access (Beta) by fall / winter
• Release toward end of year, or early next
• Mobile builds would therefore come by mid next year
We realize that this is not a very promising outlook for many of you, and we apologize again. But we would prefer to be honest and transparent as we progress. So we hope you will be patient as the game matures, though we realize that patience may be in short supply. We will be making every effort to bring you all back into greater involvement with the game through more frequent updates, more media engagement, and more frequent builds… as well as physical rewards."SOURCE
That's the most recent estimate we've got right now. Early Access towards Fall/Winter, full release around the end of 2015/beginning of 2016. I would take into account that given previous delays this is all still probably pending, but hopefully that eases your mind a little that there is a set plan moving forward, and despite complications Pixelscopic is slowly working towards delivering the best experience possible for DDrop.
In the meantime, you can catch Ryan, Coby and others working away on the weekly livestreams and keep on top of things from the Kickstarter updates. Hope this helps!