Getting the current play position would be ideal for versatility, for sure, unfortunately I don’t think you can (in BP), but I could be wrong here as I have not played around with montages very much myself.
For your use case I still don’t think you need it.
To close a completely open door, just use the Starting Position parameter to set the play position to the end of the sequence, and Play Rate to -1 and go.
You will likely need your own book-keeping variables to track whether the door is closed/opening/open/closing so you know when to reverse existing or play from start forward or from end backwards.