Actively doing this on my end. Do not confuse MPM (Mfg Process Management or Planning) and MES (Mfg Execution System). While MPMLink can assist in documentation and management of process plans, work instructions, etc, you still need a system to execute those plans and keep track of relative data. SAP, Solumina, Epsilon3 are some examples focused on the execution part but there are many others. With MPMLink, Thingworx offers connected work cell to handle execution of plans from Windchill.
As for the touch points, it depends on your dividing line between Windchill and your MES. If you use MPMLink, then you will want something that will publish those plans downstream. ESI handles this and should be preferred choice to export your process plans to your MES system. If you author somewhere else, then your integration is with the BOM, Parts and visualization data. In our case, we maintain document objects as stubs for those MES plans and test procedures in Windchill so they are linked by number and URL. Change control defers to MES system. In our case, we are exploring Thingworx as the middleware between the two systems to create a mashup but any REST service will do.
