There is likely an energy density improvement to 300Wh/kg. For example, Elon mentions maybe they can get the semi to 600mi range, up from 500. This is the same percentage improvement going from 250Wh/kg -> 300Wh/kg would create. Elon also said at autonomy day about having million mile batteries next year, which is a roughly 2 - 2.5x increase in battery life. It's too coincidental IMO for it to not be the Maxwell tech. At least from the published papers by Maxwell, these are the claims being made and they all dovetail in nicely with the hints that Elon gives. The dry electrode batteries can also take higher C rates without degrading as well according to Maxwell, so we should also see improvement in charging times.
Keep in mind, if you read more of Maxwell's quarterly reports, Tesla started working with them sometime in 2016, quite a long time ago. Over the years in earnings calls you can see that they reached milestone after milestone, first with "proof-of-concept" milestones, and in 2018 they even had a pilot line for electrode manufacturing which looked successful. There is only discussion of a single OEM working with them trying to apply their tech, and I think it's quite obvious after the fact that it was Tesla. To me, it looks like Tesla has already de-risked the Maxwell acquisition being BS. The last step looks to be going to mass production.
I believe in 2018 Q1/Q2 Maxwell Earnings, Maxwell discussed the "leading automotive OEM" they were working with on brought in their own chemistry to try with the dry electrode technology, Tesla actually brought in their cobalt free chemistry, which Elon has also hinted at.
I think in 2020 we will probably see Cobalt Free, 300Wh/kg, reduced capex resulting in 10-20% reduced costs, and also cutting Panasonic's guaranteed 10% net income, here's my estimate for cell costs, assuming currently $100/kWh
$100/ kWh, density increase to 300Wh/kg assumes for same cost, can get 20% more kWh per dollar, so 100/1.2 = $83.3/kWh
$83.3/kWh, decrease in capex for ovens/solvent/recovery, resulting in 10% cost savings, so 83.3*.90 ~= $75/kWh
$75/kWh, cutting panasonic's guaranteed net margin of 10%, so 75 - 7.5 = 67.5.
some cost reductions for removing cobalt, and the net margin of lithium suppliers (Elon mentioned going into mining, this is almost certainly for lithium), assume 0 for "margin of safety" i.e. reality is more difficult than theory.
Costs are not likely to be this low initially, but theoretically we're talking about a >30% decrease in cell costs for Tesla going forward with the ability to scale to really large numbers in terms of GWh.
At some point with this tech it probably just makes sense to drop the price of the Model 3 and make a ridiculous number of vehicles.