A ladder of promise event handlers is certainly one possibility to enforce the order of ODB writes, but I wonder if we could so something simpler:

- modbset creates an object remembering the status of the RPC request. Initially, this object receives the status "open request"
- when the rpc call got executed successfully, the callback sets the state of the above object to "request succeeded" or "request failed" (in case of error)
- if a new modbset comes BEFORE the previous one has completed, the function queues the new request in a data field of the above object
- if a rpc call finishes, and a queued new rpc request is present, it gets executed

This would be relatively easy to be implemented and keep the order of the rpc calls. Does that make sense?

Best,
Stefan