ICU does not seem to support Vertical_Orientation property from UTR #50 http://www.unicode.org/reports/tr50/#vo
Several projects that already use ICU (Firefox, next version of LibreOffice) need this property and currently have to parse the data file on their own and keep it up to date, so it would be better if ICU supported it directly.
I will ask some others about an opinion.
So far, I have not been implementing the newer properties that seem only useful in layout engines, not even UCD properties like the [Indic_Positional_Category|http://www.unicode.org/reports/tr44 ([ICU-unknown])/#Indic_Positional_Category]. There seemed very little demand, and Behdad seemed happy to provide those from inside HarfBuzz. It also separates updates to those properties from ICU update cycles, which may or may not be desirable. (HarfBuzz optionally uses ICU for Unicode normalization properties, or at least used to some time ago.)
Another problem with properties that are not blessed as [UCD properties|http://www.unicode.org/reports/tr44 ([ICU-unknown])/#Property_List_Table] is that they tend to be less stable and don't share the same name space, so API names can be problematic.
In this case, glancing at UTR !#50, there could be more "properties" that are not even called out as such – the brackets & arrows.
Review discussions with layout people once more.
See also for the Indic_* layout properties.