That's a good idea, and in principle it would work, but I don't think it's practical in the FFE.
It's generally believed that the Volt includes this capability, and that it happens automatically. In the Volt this is possible because only a small portion (about 2/3) of the battery capacity is used. Because of this extremely conservative design, battery degradation is expected to be quite small, and the portion of the total capacity that is used could be increased while still using only a small portion. GM has stated that users will not notice any decrease in range with use over the life of the car.
The FFE uses somewhere between 80% and 85% of its total capacity. Therefore there is little room to increase. Furthermore, any further increase in used percentage would serve to accelerate future degradation. So my expectation is that Ford decided on a charge window that they believed was a good compromise between range and life and this doesn't change as the battery ages.
Of course you can help things yourself in the meantime...try to restrict your use of the battery to the lower charge ranges except when needed for specific trips. As the battery ages, you can use a wider window. And as we have discussed here, there have been few if any reports of significant battery degradation among the posters on this forum. The design seems pretty good.