There are electric instant hot water systems available. The sink at my office only has a cold water line plumbed to it and a small black box heats the water right there. I've seen some in kitchens for making things like soup or coffee real quick. Not sure why they're not more common, maybe reliability/flowrate/other cost issues?
They need power and produce some noise. They take up space which may be at a premium. They require yearly-ish maintenance (running a cleaning solution through them with a small pump).
