If the code is forked, it shares the cloneparent's history - and, rather importantly, can be upgraded from upstream contemporary changes.

Datacoin does its data biz by adding a data field to the standard transaction. Namecoin does its name biz by looking at OP_RETURN data. The two variants do not interact so might well co-exist, which lends some support for extro1's earlier conjecture as to the possibility of adding Namecoin domains to Datacoin.