As is in D365 an Engineering Change Request (ECR) can only be linked to a single Engineering Change Order

Many subcontractors in the electronics business receive ECRs with a long list of products on. As is, they can only turn the ECR into a single huge ECO, which will take months of engineering work. The entire ECO must be completed before any of the changes are effectuated. To ensure traceability and a faster product cycle, they would like a feature to link the ECR into multiple ECOs. That would enable them to get product changes into production faster.

As is, the link is From ECR header to ECO header, I would suggest to add a feature to enable links between ECR lines and ECOs.