Diode networks can be - and have been - used to exfiltrate data though.
The most interesting subset of these systems are high-assurance bi-directional data paths between independent peers that are quasi-realtime. Both parties are simultaneously worried about infiltration and exfiltration. While obviously a misnomer, many people still call them diodes...
The entire domain is fascinating and less developed than you would think.
It is a genuinely fun project for someone with sufficiently sophisticated skill but I suspect there is relatively little money in it, which colors the opportunity and outcomes.
The absence of clear commercial opportunity gives the domain a weird dynamic.