Based on the Wii's set-up (if you try to load VC/WW off an SD card it actually checks if it's purchased on your console) I very highly doubt it will be possible to share downloaded 3DS stuff until it's hacked. (which isn't a guarantee; console security is getting better)
You can't just share legit game through SD card. DSiware is an example of that. Each legit game you download is encrypted with a key that only your very DSi has. Other DSis do not have your key. Your key is one-of-the-kind.
Same can be said with 3DS. Each 3DS contains an unique key that others do not have.
Well, Nintendo will surely:
a. encrypt each Virtual Console game using an assymetric crypt so it can only be decrypted on your unique 3DS unit
b. and/or, when running the game for the first time, check on Nintendo's servers whether you have really bought this game
Of course, you can try to attack this scheme by:
a. dumping decrypted WAD straight from 3DS' memory using some clever hardware
b. mimicking Nintendo's servers to always reply "YES YOU ARE ALLOWED TO PLAY THIS GAME"
I have a question about Medicat if anyone can answer.. My windows install is corrupt and wont boot. Does Medicat allow you to run DISM online or do an inlace upgrade? Trying to do some sort of repair install or recovery without a fresh installation