I guess that he's dedicating himself fully to his priority. He has achieved a lot. Words fly away but code remain.
I totally didn't expect Dan's resignation but I'm sure he's doing it because he thinks its the best decision for everyone.
As you said @ekitcho Dan's resignation doesn't stop him from further developing Steem nor did he said he would and even if he said he would I doubt he'd do it. There must be such a thing as ghost coding.
See you around @dan!