tl;dr – The link-up includes dual points accrual, IHG loyalty recognition for Mileage Club members, and two-way point exchange.
IHG Hotels & Resorts and All Nippon Airways Co. recently announced a new partnership that will significantly extend their relationship.

To date, IHG Rewards One members have been able to convert points to All Nippon Airways at a ratio of 10,000 IHG Rewards One Points to 2,000 ANA Mileage Club Miles. With this partnership, ANA Mileage Club members can now convert miles to IHG Rewards points. A ratio hasn’t yet been announced, though, given 1) the traditional airlines-to-hotel transfer ratios and 2) the relatively easy/low cost of acquiring IHG Rewards, I doubt it will be anything super compelling.
In addition to the now two-way points exchange, the partnership also includes IHG loyalty recognition for elite AMC members, as well as the ability to ‘double dip on points earning.’
With regards to the loyalty recognition, “AMC status members with Diamond + More, Diamond, Platinum or Bronze status will receive corresponding IHG One Rewards status, Diamond Elite, Platinum Elite, Gold Elite, Silver Elite – enjoying benefits such as room upgrades and late checkout at all participating IHG hotels around the world.” As of now, it doesn’t appear that status will work the other way around, and notably, it sounds like there’s at least some minimum activity required for top-tier AMC Diamond and Diamond + More members to status match: “For AMC Diamond and Diamond + More members, two elite qualifying nights are required to achieve target status.”

The dual points earning works as follows: “International travellers flying to Japan on an ANA ticketed and operated flight, can earn IHG One Rewards points in addition to ANA miles…Travellers will be able to link their loyalty accounts and benefit from double-dip earning, with IHG One Rewards points awarded based on flight distance and fare class.”

Traditionally, I haven’t spent much time with IHG’s loyalty program, though I plan to change that after I recently took out the IHG World Elite Business card from Chase. This partnership doesn’t profile (at least to me) as a major game-changer, but the dual points earning could be clutch for anyone who purchases cash fares on ANA regularly.