I really don't see MSP-ICN happening. With ATL, DTW, and SEA they have pretty much all the bases covered. I think before we see ICN-MSP we will see PDX-ICN but hey what do I know. As stated by many MSP just doesn't have the Asian O/D traffic to support such a flight something Delta looks for when adding something new.
I believe that when the Delta / Korean JV comes into effect, there will be a broad paradigm change with Delta's whole USA - Asia operation. I have to assume that any remaining USA - NRT - Asia operations will cease in the not too distant future, with this role being carried on via ICN within the JV. If the JV is able to capture any meaningful percentage of the traffic that connected through NRT, then there will need to be a considerable increase in capacity offered through ICN, such as increased gauge or increased frequency on flights such as SEA-ICN and DTW-ICN, and new markets, such as MSP-ICN.
Currently, ICN is served by SEA-ICN by 767, DTW-ICN by 747-400 and soon to start ATL-ICN by 777. Both SEA/DTW-ICN flights are already very full with passengers with destination ICN, with very few onward connections beyond ICN. All connections on these routes are in SEA / DTW, with passengers connecting to/from US destinations. There is little capacity available based on current flights for connections within Asia, so this is why such markets as MSP-ICN are likely to occur, even if operated by A330-200's.
Previous MSP-NRT flights carried many passengers connecting beyond NRT, as well as many passengers connecting at MSP to/from domestic US airports. The local MSP-Japan market may not by itself be able to sustain flights to/from Japan, but don't forget that the current MSP-HND flight continues to carry many passengers connecting at MSP to/from the midwest / central / southeast and eastern USA. MSP-HND carries loads comparable to LAX-HND. Based on all of this, I can see both MSP-HND and MSP-ICN happening in the foreseeable future.