It would not be a good thing. Firstly, it would take away the element of portability, since you have to be around adecent Internet connection. In the UK, we have "Free Public WiFi" hotspots around (though I haven't successfully connected, not even once) but the service will be sluggish as it'd hard to get a hold of bandwidth, let alone a connection.
Also, IMO the hardware isn't that great. I've had a DS Lite, DSi and a 3DS and they all had this strange 1 bar signal even if it's in the same room as the router and next to a laptop that gets a full bar of Wi-Fi.
Aside all that, I'd LOVE for OnLive to be ported to the 3DS. Though games like Assassin's Creed would have small text, I won't mind. I'm in it for the Arena, because that feature is bad-ass!