I disagree, I think Maxwell is already in the semi. Just do the math on wh/kg required and cycle rates required. Either they are using NMC cells which are lower density or they found a way to get 2500+ cycles from higher density NCA cells. The mystery of the they can get 500mi x 2000 cycles (1 million miles) from 1MWh of cells can be solved using Maxwell enabled cells. Zero Cobalt is another thing that might help the costs of building such a large pack and Maxwell would help that, thigh Jeff Dahn already published research that shows NCA could be Cobalt free and not see a big increase in degradation, though Maxwell tech would offset any loses.
As far as Roadster goes, if it's 2 100kwh packs stacked it should have 700+mi range if it uses newly updated model S tech. Maybe it's 2 80KWh packs stacked. Either way, Maxwell would help it be lighter and require less cooling for the battery, or maintain higher output for longer.