The Engels and Kautsky idea of a communist early Christianity makes the same mistake as does everyone who talks of an early Christianity. One assumes there was such a thing: one, uniform, early Christianity; purer than those that followed. Both socialists and evangelicals believe in this fallacy. The Orthodox too believe in it: an orthodox early church, before the heresies sullied it.
The communalism described in the Acts of the Apostles was only mandated within the sect in question. It did not extend to outsiders, and certainly not to other Christian sects. (As Celsus says, the Christians detested each other and abused each other constantly.)
The desire to have like forebears is understandable, both for modern socialists and modern Christians, but that desire is in the mind of the modern, and not necessarily backed up by history.