I'd like to provide some feedback about Office.EnhancedLocation and Office.LocationIdentifier when developing an Outlook add-in.
First, very happy to see improvements with this!

In my use case, I have an Office Add-in that show me all available meeting rooms (from a different Office 365 tenant). Users can add one or more of those meeting rooms as a location to the invite, through the add-on. Sending the invite, also books the room (and because of an Organization Relationship we can even use the schedule builder to view Free/Busy).
My code would use the EnhancedLocation.addAsync with body:

var locations = [
{
"id": "room1@contoso.com",
"type": Office.MailboxEnums.LocationType.Room
}
];

If room1@contoso.com is a room in our own tenant and exists in our GAL, the location gets updated with the displayName of the room "Room 1 - 6 persons".
If it is a room in the other tenant (and thus doesn't exist in our GAL), it just shows the e-mail address as location.

Preferrably, I would like to do something like:

var locations = [
{
"id": "room1@contoso.com",
"displayName": "Room 1 - 6 persons",
"type": Office.MailboxEnums.LocationType.Room
}
];

With custom locations, they could also use the displayName property and have their own "unique identifier" in the id field. The API would still be consistent.
And with rooms that do exist in the GAL, it could still resolve first with GAL and use the displayName is a fallback mechanism.

I send the description my team is having with the json integration with Office API 365.

We want to send an email with inline attachments through the JSON API.

With that objective, what we are doing:

1. Create an empty draft message;
2. Send the several inline attachments;
3. Update the body of the draft message (with cid images inline);
4. Send the message;

What is are our issue with the API?

We are unable to set the "ContentType" properties when we submit the attachments to the Office API 365.
Despite the "ContentType" we send, it is always null.

We are using the following API: POST https://outlook.office365.com/api/v1.0/me/messages/{message_id}/attachments

That's the reason we think that despite the inline image then it is found in the body, it cannot be displayed because the contenttype it is not set correctly.

Please give us some direction.