Steve, your comment that states are "moving toward electric over hydraulic as the new mandate" puzzles me. Are states enforcing separate breaking systems?
I just reviewed the trailering laws on a number of sites. The best seems to be AAA:
http://drivinglaws.aaa.com/laws/trailer-brakes/
I don't see any mandating electric over hydraulic. A few have the wording such as this:
In any combination of motor vehicles, means shall be provided for applying the trailer or semitrailer brakes in approximate synchronism with the brakes on the towing vehicles and creating the required braking effort on the wheels of the rear-most vehicle at the fastest rate, or means shall be provided for applying the braking effort first on the rearmost vehicle equipped with brakes.
or
Every trailer of a GVW of 3,000 lbs. or more must be equipped with a separate, auxiliary means of applying the brakes on the trailer from the cab of the towing vehicle. (Iowa)
Then there are rules such as
"Every trailer must have parking brakes adequate to hold the vehicle on any grade it is operated, under all conditions of loading and on a surface free from snow, ice, or loose material."
Rather than assuming that electric over hydraulic is mandated, it appears that a few jurisdictions are requiring that the trailer brakes can be applied separately from the tow vehicle brakes--in the case cited, more rapidly or applying breaking effort on the rear most vehicle. Unless there is a separate braking system for the semi trailers from the tractor, that would seem to create a problem for most over the road commercial 53 foot trailers and trailers in tow such as triple towed rigs.
It also will create a major issue for autos which are towed behind RV's and treated as trailers in many states. There are tens of thousands, if not hundreds of thousands of boat trailers which do not have this type of system.
I think that electric over hydraulic is great--but it does substantially increase the cost of the braking system, and assumes that the tow vehicle is set up for that type of rig, and is not necessary for the lighter boats such as a C Dory 16, 19 or even the 22's.
I guess I'll just stay in Florida, where I only have to have brakes on both axels if the trailer is over 3000 lbs. No parking brake on the boat trailer, and no separate way to apply the brakes, or apply the rear most brakes first.