the ignition on my bike was relocated in this fashion when i bought it. keep in mind that since you're mounting it on the frontend of the bike, the wires will have to bend and flex when you turn the handlebars. here are the problems i have had with the setup:
the wires have been abraded by vibrating and rubbing against the front edge of the gas tank (in the center where the arch is). and, no, my bike doesn't vibrate excessively. it has not yet worn through as i have proactively wrapped electrical tape over this "high-traffic" area. i check it often and replace the tape when i see that it is down to one or two layers.
i have also had one wire come un-soldered from the back of the ignition. this was a PITA to fix.
if you have anything attached to your ignition key (split ring, key fob, house key, etc.) it'll rattle and buzz obnoxiously on long trips because it isn't allowed to dangle free as in the frame-mount setup.
upward-facing ignition more likely to acquire water in it. mine came with a chrome cap on a hinge to protect the ignition when they key isn't in it... so the cap and hinge rusted instead. great.
all-in-all, having the key here has been a pain in the butt rather than a convenience.
so i'm going to move it back down under the tank onto the frame as soon as i get a Round Tuit. and some parts.