I think this is confused over the origin of the Sarafand, which was a military type (with civil potential). Oswald Short thought he could build an aircraft with better performance than the Dornier Do.X at a fraction of the size, and that this would be imperially significant - I suspect he was envisaging the potential we subsequently saw with the Empire boats. He talked Trenchard, then Chief of the Air Staff, and not a flying boat fan, into building it. The military requirement, R.6/28 emerged because the tender had to go out to other companies as well, and Supermarine got a Type 179 contract as a result. but the Sarafand was built for the RAF, not Imperial Airways. The civil requirement was 20/28 Mediterranean Civil Transport, which the Type 179 was redesigned for (i.e. there are two different 179s). That seems to have suffered from requirement creep and was cancelled in 1932.
There seems to be a potential POD at this point. Trenchard resigned as Chief of the Air Staff in late 1928 as he thought he had done all he could in the role. The cabinet took a while to accept and he wasn't officially retired until 1st January, 1930. R.101 crashes in October 1930, leaving the country needing a new Air Minister to replace Lord Thompson, who had been behind the civil side of the requirement. So what happens if Trenchard is offered the job? Trenchard had a reputation for being frugal, he'd paid for the Sarafand, and Imperial Airways needs a long range 15 seater aircraft to cover Mirabella Bay in Crete to Alexandria, because the Italians have closed their ports to Imperial Airlines (they reopened them, but could potentially close them again). The actual aircraft built to cover it is the Short Kent, and construction didn't start until October 1930, with service entry in May. The Sarafand couldn't cover that, it's still being designed at this point, but adapting it would have been trivial, it had the cabin space. The confluence of multiple factors around Shorts, large seaplanes, Imperial Airways and the empire routes is one Trenchard can't miss, because he's personally involved or professionally responsible for all of them. Imperial Airways could be picky about their aircraft requirements, but I don't see that going down well with Trenchard. What this does is give you the potential to bring the Empire Air Mail Scheme and the requirement for the Empire boats as a smaller Sarafand/improved Kent forward from the end of 1934 to the start of 1931 and R.2/33 for the Sunderland along with it (Trenchard will like the frugality of a common design).
I don't think a monoplane Sarafand will fly. The increase in size is risk enough, the Sarafand is basically a scaled up Rangoon, and Shorts haven't built a monoplane since the tiny Cockle in 1924. There's no way Oswald Short would have talked Trenchard into backing a monoplane Sarafand.
WRT the Knuckleduster, I don't think you can bend R.24/31 to fit the Sunderland. R.24/31 was specifically for a two-engined flying boat, not a heavier 3 or 4 engined type. The Knuckleduster got in as an experimental single prototype to demonstrate both a monoplane flying boat and steam-cooled engines. OTOH a conventionally engined Knuckleduster with less-draggy radiators would have been interesting, and if you can bring forward the Empire/Sunderland requirements to 1931 as proposed above then you don't need to replace the Knuckleduster and it can potentially function as a demonstrator for the Empire/Sunderland's planing bottom, much as one of the Scion Seniors was later used.