I'd argue that this is not an issue from a technical perspective, which would halt open hardware endeavours.
The precision is mainly a problem regarding the used motors / actuation system, which in turn is "just" a money issue, but the hardware is there. Paper handling is pretty easy.
I don't know how complicated it would be to create ink or laser cartridges, but given that there are a lot of 3rd party vendors who offer refill services, I suppose it is manageable.
My guess for the reason why there is no open hardware 2D printer yet is, because nobody has seriously started such a project yet.