when load power consumption starts decreasing or battery technology improves significantly?
currently load power consumption is pretty stable in notebooks due to thermal constraints and such
battery sizes also are relatively stable
so battery life improvements during load haven't been that great in general
software/driver based improvements can improve battery life as well. hd264/ high def used to completely load processors which would decrease battery life (but nowadays, "high def" video isn't considered heavy load is it? since it doesn't heavily load anything for the most part)
apple's ios due to all the proprietary hardware/software allow for optimizations in power consumption giving it improved battery life relative to windows
so it's pretty hard to estimate when 10 hours under load will be achievable
i would guess when the future breakthroughs in battery technology are implemented (maybe 10-20 years?), since people are using laptops as portable desktops and thus need more powerful processors