I'll say up front that my system is running an early version of SPS 10 and there will be lots of extensions to CDS in SPS 10 for better integration of standard SQL functions. That said, I'm able to use the CURRENT_UTCTIMESTAMP as the default just fine in my system. Looks like this is a feature which is coming soon.
namespace playground;
@Schema: 'PLAYGROUND'
context scn {
@Catalog.tableType: #COLUMN
entity Users {
key ID : Integer;
Name : String(20) not null;
updatedDt: UTCDateTime default CURRENT_UTCTIMESTAMP;
};
};


