That's not a system I'd want to trust for a heavy bike on a long descent! Braking with a disc can generate quite a bit of heat. Having the hydraulic fluid which actuates the brake in such close proximity to the caliper would have me worried that you might overheat the brake fluid and experience dramatic brake fade during a long descent. Personally, I'd stick with a tried and true MTB-style hydraulic system, if you need hydraulics: fluid reservoir near the brake lever, connected by a long hose to the caliper.