I think the technically correct feature request would be: “Add an Obsidian command for ‘toggle strikethrough for selection’”. This is how there are assignable hotkeys for bold and italic currently.
Just so everyone knows, an excellent workaround is to toggle on “Autopair markdown syntax” in Editor settings. Then you can select the text you want to strikethrough and tap ~ twice for the desired outcome.
A hotkey would save an additional one keypress of time.