I know that a lot of people like 'proper' locos like 56's, but lets be realistic here.
The class 56s were introduced around what, 1976 to to early 80's was it? Only remember because 1976 was the year I joined British Rail! That makes the oldest one 35 years old (and me considerably older unfortunately). They were not the most reliable even when in their prime, a pain to repair (particularly the exhaust system) and are long in the tooth. Why would a freight company use 56s when there are far more cost effective locos available? Yes I know drivers generally liked them, and they were good haulers, but at what cost?
Preserving one or two is one thing, but adding all the modern safety systems (TPWS GSM-R etc) and getting them up to speed mechanically is just not a realistic aspiration for day-to-day mail line operations.
Quite a bit of passenger stock that is newer than the 56s has been scrapped, why should freight haulage be thought of in different terms to passenger stock?
"What a Waste?" I don't think so.
Let the flaming commence!!