You would have to increase the weight of the bolt a lot to slow down the cyclic rate enough to make it a practical weapon. That is the main reason why this sort of thing rarely works. The Beretta 93r, which I shot quite a lot, fired its three round burst at a rate of 1100 rpm.
Parker Hale got their prototype Bushmaster, which I also shot, down to 180, which they reckoned was the highest controllable rate of fully automatic fire for a weapon to be fired in a single or two handed grip. They did it by getting the weapon to fire itself electronically in semi automatic mode while the trigger was depressed. Very cunning, very expensive and impracticable in 1914. Controllable, double-handed 3-4 round bursts into the black of a PL7 were possible at 25 yds.
I suppose someone might try it, find out it does not work, and webley get word of it leading to them starting work on a real sub machine gun.
Remember that OTL the SMG came out of the idea for a lighter machine gun, not a more powerful pistol.
The 32 scorpion idea is practicable, but not really a a front line combat weapon. .32 ACP is a fairly weedy proposition when one is used to .455. See Colonel Cooper's comments on SMGs! Better to start from scratch. .380, 9mm browning long etc are all good cartridges for a blowback sub machine gun.