Blizzard has no plans to release Overwatch on the Switch last I checked.Pack 1 - Joker (Persona 5) releasing Q1 2019 w/ Persona 5: Rouge announcement for May 2019
Pack 2 - Dante (DmC 5 Ver.) announced in the fortnight around March release of DMC 5, coming out Q2 2019
Pack 3 - Tracer (Overwatch, to launch with Overwatch switch, announced at E3 2019
Pack 4 - 2B (NieR Automata), also announced at E3 2019 with NieR Automata port
Pack 5 - Undecided, most likely ending SSMBU DLC with Goku
2B seems super possible.
That and Sora (who's been highly requested)
I can't possibly guess what upcoming releases they could use smash newcomers to tie the release with.