Importing Descriptions/Comments into Reports

If I understand the ask correctly, you do not just want to concatenate together the existing Entity + existing U1 descriptions that are on those members today.  If I understand you correctly, you are saying that when Entity 1 uses U1 the description may be one thing but if Entity 2 uses U1 the description is something else.  Is that correct?

If so I have had this on another project where we needed to vary the U1 descriptions based on how they were being used by various entities.  The way we solved was to have a custom table that stored the U1 descriptions per each Entity combination.  Then in cube views or reports we had to use an XFBR string to do a lookup against that custom table and pull back a dynamic description.  The XFBR passes in the entity and U1 members and bumps those up against the lookup custom table to pull back the new U1 description.

OS has language tables that are culture specific, but having different language descriptions did not solve our issue of when combinations of entity and U1 were used, we wanted specific U1 descriptions.  

If the issue resolved around Entity and UDs in theory, you may be able to put each entity into it's own sub-cube and use extensibility to show UD descriptions specific to each entity, but this would probably be overkill and a maintenance nightmare.

I agree with T_Kress except I would use XFStrings rather than a custom table. XFStrings do not have to be in different languages (Is Localizable = False). The problem I have with a custom table is that it is not part of an application extract and so is easily overlooked. You can manage a custom table in Excel (XFT format) but you will need a process for extracting and reviewing the existing data. XFStrings are part of Workspaces/Dashboards so are easily reviewed, added to a dashboard etc.

Under Transformation Rules there is a Lookup rule group. This lookup table can be referenced in XFBRs as well. I'd imagine there may be some way to utilize that where the Source is the combination of certain dimensions, and the Target would be the String.