Whoooaa Dafydd, please back off here, the direction of this post is starting to sound like some LAMEs who don't want us to work on the aircraft that WE built. Some have actually approached CASA about this. We are NOT FAR 23 aircraft & never will be, however that is not to say we shouldn't use best industry practice where possible.
IMO (and industry practice, etc,etc) simply put, the Starter should have a Solenoid & the Battery have it's Isolator (switch, toggle or otherwise) too.
IF anyone has essential equipment that needs to be on all the time eg EFI systems, then one method could be to have switched/fused power direct from the battery so that when the battery Isolator is off the required systems to keep the engine running are still powered up. In an emergency, or if a Starter is stuck on, then disconnecting the battery for other items like flaps, lights & even radios are not really needed in most cases.
Jake J