A4 -
was Orion ever considered as a Shackleton replacement
.
In a word - No.
As a JO I held prior to my Shackleton course at HQ Coastal Command, and one of my jobs was to look after the Archives. As such I also had the opportunity to file (and read) a lot of the documents that came in - including those regarding the Shackleton replacement(s). Right from the beginning there was one overriding Treasury edict - that whatever replaced it had to be British built and designed, to save spending any money outside of the UK. In addition when the replacement was first puit out to tender, it was the principle in MOD that UK forces only operated UK equipment (with a few very small exceptions). There was also the requirement for at least three engines (see HS 800 and Avro 776), as jets were still not considered reliable enough for twin engine ops a long way from land!
Of note, it seemed it was also the dead hand of the Treasury that led to the Mk 3 Shackleton as a Mk 2 replacement. The original plans were for a new airframe, but the Treasury would only accept an upgrade to the existing airframe - so although Avro did their best, that's what we got.
Unfortunately this wonderful treasure trove of documents and memorabilia going back to the formation of the Command and all the WW2 action reports and reviews was stored in the Headquarters building, which included the Officers' Mess. It was destroyed by fire early in 1969.