Castle doctrine not only states you have no duty to retreat in your home, it also creates the presumption that anyone forcibly entering your home that has no right to be there puts you in grave danger at risk of serious bodily injury or death. Your proposal eliminates the presumption of imminent danger/death in one’s home (castle doctrine) and forces the lone homeowner to bear the burden of showing how they were in fact in danger.
The purpose of SYG is not to mete out swift justice nor do its supporters believe our ability to punish lawbreakers is inadequate. The purpose is not to shift the role of the justice system to the individual. The was well articulated by Una Person in the other SYG thread:
And myself, from later in that thread:
In FL at least, the person asserting the SYG defense must do so based on a preponderance of the evidence. But even in simple self defense cases, where there is a plausible claim the burden to show that the killing was not in fact self defense should rest on the prosecution, and the standard should be beyond a reasonable doubt.