It wouldn't be impossible for them to do, but considering the license fees for whichever system, for example, DTS, they'd have to convert the output to, not to mention the necessary A-to-D converters needed to accomplish the deed, and to include the HDMI output, the price of the SM would be, necessarily, much higher. Is there really a market for that extra circuitry to be added to an already excellent piece?
On that note, Involve has a preamp in the works that will include Surround Master circuitry. I don't know for certain if it will also include HDMI in/out connections; As far as I know, it's an all-analog device, possibly including a two-channel-in Toslink optical input, that could be fed from a CD/DVD player for playing stereo CD's through the SM circuitry for enhancement, or matrix-encoded discs for proper decoding. Involve are also looking to license their SM circuitry to other hardware manufacturers, for inclusion in their receivers and processors. At the same time, there's a bit of a push for said manufacturers to, once again, include multichannel analog inputs on their products.
I use my SM with a Denon AVR-3300 receiver, from back in 2000. It has Dolby Digital, DTS, Pro-Logic 1, and analog multichannel inputs. Those inputs are shared, via a switchbox, with a DVD/DVD-A/SACD player, and my CD-4 demodulator. It works, and it's terrific. The receiver still works perfectly, and sounds as good as the day I got it.