Based on the postscript on the website.
Battle pass 2020:
The toy butcher(Pudge persona. Probably with dc hook or arcana)
The disciple's path(Anti-mage persona. Probably with bashers)
The one true king(Wraith King arcana)
Eminence of Ristul(Queen of pain arcana)
Compass of the rising gale(Windranger arcana)
Battle pass 2019:
Planetfall(Earthshaker arcana)
Battle pass 2018:
Promise of eminent reveal(
Battle pass 2017:
Nothing(maybe in 2017 valve did not expect to sell cosmetics again)
Battle pass 2016:
Legacy of the fallen legion(Legion Commander. If they expected)
Also i think that all content from this bp will be available either in the next battle pass or in the store after this ends.
Source: https://www.reddit.com/r/DotA2/comments/o7u4on/a_list_of_items_that_may_appear_in_future_bps/