OP: your point about the 14 day returns period is also valid here. If Apple DO release an updated iMac within the grace period, you can return it and get the new model.
I highly recommend the Pegasus unit for external storage and real-time editing. It comes in R4 (4TB) R8 (8TB) and if you are super wealthy R12 varieties...Thunderbolt connectivity allows for real time edits, and I have mine split into two arrays, one for archival purposes, the other for projects I'm currently working on.
Hope you get the Mac you want..🙂