Other than a nonstop to HKG and (from DTW,is there another nonstop to an Asian destination?)) Delta connects to non-Japan Asian destinations via its NRT hub. There is already a "direct" ATL-SIN (which goes via NRT and requires an aircraft change too). Essentially, it's ATL-NRT. Delta might start "direct" services to other Asian destinations, but it does not make things better.
ATL is fartehr from NRT than any other DL gateway ( about an hour further than DTW-NRT).
What will happen to DTW, if DL moves its US-NRT/ASia flights to ATL? It would be the demise of DTW as an international gateway. The Asian market that DL inherited from NW prefers flying via DTW. There are some DL flyers who are used to flying through ATL and might want to fly ATL-NRT-Asia.
I think DL should keep DTW as the main gateway to Asia.