Regenerative braking as it is usually called was available on some of the brushed speed controls. Tekin 411P for example, from about 1990, had it and advertised it prominently. Regen braking made a significant difference with the much lower capacity batteries of the time. It was a deal breaker in 1/12 onroad which was perhaps the most impacted by limited batteries, the fast guys didn’t use full throttle, or at least very sparingly, or they would dump. If I remember correctly a couple laps was immediately gained compared to previous ESCs.

Haven’t seen it mentioned or advertised with brushless, there was discussion that it wasn’t done when brushless first became popular. At least partly because it added a lot of complexity to a unit that was already far more complex than we previously had as I remember it. Although there may be some stray amount as mentioned.

Off subject a touch, full size electric autos do implement regen braking.