If it’s as good as it sounds, I would like to see it in the SR20. Apart from anything else, it would solve the ADF indicator problem (since it has two RMI type pointers).
I emailed Cirrus asking about the ADF and the Sandel HSI. They answered me promptly and at length.
The nutshell version is that the ADF installation has not yet been engineered by Cirrus (so if you want the ADF/DME/2nd ALT option, you will be waiting) and they are looking closely at the Sandel HSI, but there is quite a lot of work to engineer and certify it, so don’t be too impatient.