As a trike rider since 2007 I have some points.
1. Assuming two wheels at the front forget a rear brake for anything but parking. Both my tadpoles, the QNT with SA drum brakes and the Trail with Avid BB7 discs will lift the rear wheel clear off the ground under hard braking. A rear brake used as a drag brake on 20%+ hills will tend to lock up and once locked will cause you severe problems.
2. Linked brakes with one lever may sound good, but in effect limits your braking to the grip of the lighter wheel. You rightly point out that you will unload the inner wheel at speed.
3. Brake Steer, the tendency of a trike to turn towards the strongest (or only brake applied) brake is controlled by clever design, my QNT will pull up with very little and easily corrected brake steer with only one brake even when that brake is on the point of locking up. (That is when it is exerting maximum deceleration.)
4. The ability to lightly drag the brake in the inside wheel as you are already making a sharp fast turn makes the trike turn into the corner, even on the QNT this is worth doing! Also when the inside wheel stops rotating you know you have lifted that wheel clear of the road. A clear sign to ease off!
5. For a Delta, like my Kettwiesel, a front brake has limited use as the front wheel is very lightly loaded and would lock up before weight transference to the front occurs. My BB7 equipped Kett' will brake much like an upright bike whereas the tadpoles will out brake any upright in any conditions.
6. Deltas tend to have more brake steer, it is very useful for fast cornering! But less useful unless you can easily modulate the individual brakes on the rear wheels. This applies less so on a tadpole but I for one wouldn't entertain linking the brakes as with one wheel on gravel and the other on clean tarmac the trike will turn away from the gravel, hard, being able to ease the brake on the gripping wheel keeps you straight.
Hope this helps.
