The only meaningful difference I’d expect anyone to care about is the recharge time of the 20Ah to come down. It’s not stated but my guess is 30 mins faster.
I’m only highlighting now so anyone who buys the current 18W do so with the knowledge and so factor price paid and urgency. By all means help empty stock at discounted prices of the 18W versions, as these deals appear next days and weeks.
Critical is if you get these 20W versions you pair in advance with 20W chargers like the upgraded Nano 20W. I expect the other 18W Powerport to all get upgraded, like the dual 18W to dual 20W.
Example two pack of the 20W Nano
Example 65W wall charger with 20W port, observe the shipping dates match so there is some logic of 20W across the board if you pay attention to detail.
Just don’t write in the future any buyer’s regret.