In an emergency whatever works, works. I guess the question is, will it work?
As far as IFR engine out, it sounds like a reasonable last resort procedure, with the following understandings (and I’m sure you’ve thought of them already):
The airport waypoint will not necessairily correspond to a runway centerline, so even if everything works perfectly you might not be lined up when you break out. (This assumes an airport with no IAP; otherwise you could call the IAP up from the GPS if you could find one that corresponds to your inbound course.)
Of course, if there are any obstacles in the area (terrain, towers, other aircraft, etc.) the procedure will not ensure that you clear them.
In any scenario other than engine out, you’d have to weigh the cost of delay against the risk of the “homebrew” approach.
All that said, any forethought about what you’d do in an emegrency situation is valuable! I’m sure having thought about things like descent rates, airspeeds, etc., in advance will pay off when they’re needed in the heat of battle.
I would be interested in the forum’s collective perspectives on using the 430/420 and its map to get down in an emergency under low-medium IFR contitions: engine out, passenger or pilot medical, ILS LOC/glideslope failure, etc. I have thought this through for my 260se: trim for 60-65 KIAS, fly a “normal” pattern, subtract half the runway length from the “direct-to airport” distance to judge approximate distance from the threshold, and multiply groundspeed by 5 to get a ~3 degree descent or ~6 for a 4 degree descent. At my slow approach speed I can be a little slack about needing to touch down just after the threshold…the SR20 shouldn’t be too different, maybe an extra 15 kt approach speed.