We don't support FILESTREAM, like we also don't support BFILE on oracle. The main issue is that when fetching the data with a column containing a FILESTREAM or BFILE type, the entity isn't fetched when the data is read: it's to be read separately, so this creates a situation where an entity object has to be returned but it can't be returned yet because the filestream /bfile hasn't been read yet, however reading it later on would require a db connection, which is also not ideal/perhaps not even possible (entity is higher up the call stack)
Our recommendation is to use varbinary(max) fields on sqlserver and BLOB fields on oracle instead: one can fetch these fields later on and exclude them from the fetch process using the excluded fields feature.
