I have a 3phase instalation at home and is certain that one of the phases could be free to feed the charger (for example, if L1 is highly loaded by a pump or any other appliance, and L2 is also loaded by something else, while L3 is at that time less loaded, it would be interesting to have some kind of phase selection feature that could simply connect the charger to that phase and use all the available current from that "free" phase, instead being limited by the current available at a overloaded phase.
Is this feature possible?
Possible? Yes. The better questions would be whether it's practical and meets local electrical code requirements. I would wager that the answer those questions would be no. The monitoring of the load current on each of the three phases is very doable. EVSE charge management solutions do this already in some installations. They monitor the overall load on the system and use that information too vary the maximum charge limit on one or more EVSEs. This information could be used to switch a load between phases, but this is where the bigger challenge arises. You need to ensure that you can't accidentally short one of the phases when making the switch. This generally means a momentary break in power to the EVSE. Given that, you probably want to avoid switching in the middle of a charge cycle. You probably also want to have some hysteresis or minimum time between switching (or both) built into the system so that you don't have the system switching back and forth when two of the phases are at very similar load. None of this talks about potential failure modes and how they may need to be handled safely. Realistically, I can't see this kind of a system providing enough value in the real world - especially for a home system. Your service should be sized to meet certain code requirements for your local jurisdiction. Those requirements generally mean that the likelihood of you exceeding the maximum current for your service before tripping breakers on one or more branch circuits is extremely unlikely under normal use. If this is likely, it probably means that your service is undersized and probably not meeting your local electrical code requirements. If you have a 3 phase service with a number of single phase loads connected to it, they should have been set up to roughly balance the potential single phase loads across the 3 phases. Would you go to this kind of trouble for an oven or an air conditioner? If not, then makes the cost/benefit analysis different for an EVSE?