Based on personal driving experiences, the regen/brake sys mixing is clearly software job, or we can say fly-by-tweakable-wire. The dynamics of brake pedal feedback can tell you sth. different than conventional gas cars. And that's why Nissan can come up with the B mode so easily.
But there is another point, when we go back to the fundamentals, there's more to look into than heavier regen is better.
In theory , from the energy efficiency point of view, the best scenario is no braking at all --which everyone knows; and all energy goes to regen when you have to brake. There are two problems in this part.
1. how much energy was allowed to goto regen sys. Nissan has addressed this with B-mode, or, in the far future, might allow you to tweak this limit to whatever you want, which i doubt due to safety concerns.
2. efficiency of Regen sys. Regen sys would save part of the energy lost to friction heat, but will never be 100%. regen sys has it's own efficiency limit even you input 100% braking energy into it. This would compromise more aggressive regen. tweaking.
When we come back to practical driving, the best efficiency strategy is not using regen as much as possible, but keep the car moving at constant speed as long as you can and use both pedals to achieve that. Like the most talked about long distance downhill situation, as long as the traffic permits, regen-off would be more efficient than regen invovled.
You use regen/brake, only when you have to - for your safety.
For the part we have to use brake, to satisfy everyone, we might need self-learning sys. to adapt to personal habit, then come up with the best tweak for that person--hey, we probably have had automatic driving machine for that purpose.