I mean, Elon explicitly said they can't, but you do you.
Elon Musk on Twitter
I get when folks doubt Elon because he's promising some future feature that doesn't work yet... but here he's simply saying existing battery tech can't physically fit in a car that exists and has known dimensions.
So no 100kwh pack unless they redesign the car (not happening barely 2 years into production especially with GF3 just getting going) or they switch to a different, denser, battery tech (which would happen in the more expensive S/X first anyway as they've made a very very obvious effort to keep S range ahead of the the 3)
So if I had to be cassandra about it I'd say at BEST you could:
Look for newer,denser, battery tech in the S mid 2020 when Plaid comes along.... then showing up in Roadster and X maybe 2021 or very end of 2020 depending how they can ramp the new battery production (Musk specifically said X/Roadster later)
And then that in the 3/Y maybe 2022 since the 3 will be ~5 years old by then and a bit of a facelift wouldn't hurt anyway... plus 2022 is when I expect
actual competitors will be showing up in decent numbers so another generational tech jump would make sense.
and at worst:
If Plaid comes out and it's just S/X/Roadster using 2170 cells (which are about 50% denser than the 18650 they use now).... you're looking at even longer to see 100kwh in a 3/Y.
And given they probably would want a longer return on investment on 2170s than just a couple years of 3 production, that seems even more likely than the best case scenario.
The wildcard there is how quick they get maxwell tech into a production battery.