I believe the Cirrus uses the undercarriage as an inherent part of energy absorbing structure
True. And guess what... A twin typically has a retractable undercarriage.
So it's not just a matter of adding the BRS (in itself quite a complex undertaking) but you also need to redesign the undercarriage so that it deploys automatically upon BRS deployment (and how do you do that in a dual engine failure with possibly no hydraulics available?), and that it can handle its part of the vertical impact load.
So in theory it may sound like a good idea but there are some construction details and weight penalties that will make it very hard to implement.