In previous discussions on this topic I provided what is for me the most compelling argument against the "last expression" rule:
Basically it boils down to that result builders already gave dangling expressions a different meaning (namely, that all of them get used, not just the last one), and since there is no visual indicator that a result builder is in effect in a given context, giving dangling expressions a fundamentally different meaning in non-result-builder contexts feels to me like it could be disastrous for readability.