Hmmmm. If you're not using the wing for landing and takeoffs, the heavy wing loading wouldn't be a factor if you keep the speed up and don't try to do high-G maneuvers. Of course, the speed is the main problem. The model may need a high-enough speed to make the transition impractical.

One thing to remember is that most aircraft don't need a wing as large as they do in order to fly controllably. Witness the cruise missiles with their tiny wings. You need the large wing area in order to make takeoff, landing, and slow flight have reasonable airspeeds. If you can takeoff on the rotors and then have them rotate forward at a rate that allows the airspeed to build up well, you can likely live with the high wing loading. Just remember, though, that the high wing loading brings about a high stall speed, so you'll need to be rather careful in turns. Aerobatics would be out, of course.

As far as lengthening the span, do remember that you may need to change materials for the spar or go with a thicker section. The longer span will put increased bending loads in the inner portion, and you have to allow for that. Also remeber that the pods on the wingtips add bending loads once the weight is on the wheels. A hard touchdown will put downward 'G' loads on the wings that will be amazingly high...maybe even higher than in-flight positive 'G' loads in a turn or pullup.

Interesting project!