DCASonex wrote: Does not look simple, and likely to add more weight than we would want, but no harm in discussion.
In theory, the installation of a BRS could be very similar to the one on the Zenith 601/650, shown here.
http://zenair.weebly.com/ballistic-parachute-kits.html. A Sonex would probably need a swing-back canopy if done this way, with quick-disconnect points for the canopy located inside just to be sure (wouldn't want to drop into the water and then not be able to get out.
All that is in theory. I don't think it's a good idea.
The weight is something to be considered carefully.
Rather than considering the BRS in isolation, we should think of the problem in terms of total risk management. With two average-size people aboard my plane and full fuel, I have about 35-40 lbs of available cargo weight. With a BRS (new attachment points and local "beefing up", cables, canopy, rocket, actuator mechanism, a new break-away panel and frame, etc) I could very well use all of that up. So in many cases, we'll be leaving stuff on the ground that we could take if we didn't have a BRS. Like fuel. Or a GPS/emergency radio. Etc. I wonder which would have saved more people, looking back at accident stats: the BRS or another gallon of fuel, a radio, a fire extinguider, or a lot of other things that couldn't be carried if we load up with a BRS. Just the small but measurable incremental loss of climb rate with the weight of a BRS aboard has a safety cost.
And the added BRS weight would probably be behind the CG--not a good place for most Sonexes. How does an increase risk in out-of-limits aft CG affect total safety? Not well. Further reduction in useable fuel (because some of it is now needed forward as ballast--also not good).
With a BRS, the Sonex would become either a two person plane with reduced fuel and no baggage, or a one person acft with no acro (CG limits, impractically small fuel allowance at acro weights for most pilots). That's a lot of utility to give up.
As Joe said--Sonex has looked at this and didn't see how it could be made to work well. I'd say if a person wants a BRS, it would be best to look for an acft design that included that provision from the start, or which can be made to accept it, But even then--look at total risk management. The Sonex design includes a lot of safety features (low stall speed, robust structure, very tough fuel cell, good handling, predictable and docile stall behavior, etc) that may do more to mitigate total risk than a BRS on another airplane.
Just my 2 cents.