Why would that be? If the battery cannot take any more change, would not the system would just revert to normal, non-regen-style braking and dissipate the energy as heat, as in most non-hybrid cars? Trying to manually manage your battery charge may be fun for a bit, but it would also add to your driving tasks and become a bother after a while. I am not even sure how you would do it, since your battery charge level is not very apparent from what I have seen.

One other question is maintenance related. Would you rather replace brake pads or the generator/charging system? Over time, in constant L mode, it seems you will work your charging system a good bit more than it might be designed for. Of course, none of us has had an Escape long enough to really test this theory out, but seems there might be a design reason why they have two modes rather than one. Same goes for the Prius I guess, so maybe someone in that forum can speak to the longer term experience.