My Si needs the clutch pedal depressed before the engine can start, any aftermarket system would have to bypass the clutch interlock switch, it could be done but that could be a safety concern.
This, exactly. Not only would the car have to be in neutral and the parking brake engaged for this to be safe, you'd have to bypass the clutch... Which may even be illegal, depending on where you live (pretty sure it would be for me).
Now it's unlikely to get you into trouble, as I don't even think it's something they check during annual vehicle inspection (which is mostly emissions oriented, plus checking things like the turn signals and brake lights being operational), and if anybody drove the car normally (i.e., pressing in the clutch before starting the ignition) they almost certainly wouldn't notice that it could've been done without pressing in the clutch, LOL.
However, should you get into an accident and it came out that you intentionally defeated a factory-built and most likely legally required safety mechanism, that could be Pretty Bad.
I mean, consider that parking in gear it is NOT something the car requires - nor is the parking brake auto-engaged when you kill the ignition. From the factory, the clutch safety switch is really the ONLY thing preventing the car from just launching on ignition and driving off at speed.
I assume the remote start mechanisms discussed here somehow build in requirements for the car to be in neutral, parking brake on, etc., but if that aftermarket safety mechanism were to fail, it's not impossible that the insurance company would make a stink about it.