This post is a collection of official and unofficial rumors about the OWL rosters, so it could be completely wrong. But I find it interesting to think about potential rosters for the OWL teams, so I figured I would start this thread here as well.
To look at confirmed rosters only, check remiska's thread (https://www.over.gg/5409/overwatch-league-teams).
Boston - Not official
- NotE
Gamsu
DreamKazper
Mistakes
Snow
Striker
Fischer
Architect and Kalios are rumored to be in negotiation
New York Excelsior - Not official - Signed LW Blue's whole roster
- Mek0
janus
Mano
Fl0w3r
Saebyeolbe
Pine
JJoNak
ArK
Libero
London Spitfires - Signed KongDoo Panthera's whole roster. Cloud9's franchise.
- Void
Fissure
birdring
Rascal
wakawaka
Bdosin
Quatermain
Nus
Los Angeles - Immortal's franchise- Not all confirmed
- Fate
numlocked
GrimReality
Agilities
SoOn
Verbo
Kariv
uNKOE
envy
Los Angeles Gladiators - Not Official
- Bischu
iRemix
Surefour
Miami Mayhem - Not official - Misfits Roster
- CWoosH
TviQ
Logix
Zebbosai
Zuppeh
Manneten
San Francisco Shock - NRG's franchise
- super
nomy
iddqd
sinatraa
sleepy
dhaK
babybay
Danteh
Dallas Fuel - EnVyUs' franchise
- cocco
Taimou
EFFECT
Seagull
chipshajen
HarryHook
Mickie
Houston - Not official - OpTic's franchise
- coolmatt69
Muma
Clockwork
Mendokusaii
Boink
Bani
Philadelphia - Unknown
- Carpe is rumored to be in negotiation
Shanghai Dragons - Unknown
Seoul Dynasty - Signed Lunatic Hai's whole roster - Unconfirmed
- Miro
xepheR
EscA
Munchkin
ryujehong
tobi
zunba
Gido
Fleta
Wekeed is under trial
Other
- One Korean team is rumored to be in negotiation with an OWL team
- Boombox is in OWL, but it is not clear for which team yet
Sources:
http://www.espn.com/esports/story/_/id/20954529/sources-immortals-sign-unkoe-soon-numlocked-la-overwatch-franchise
https://www.reddit.com/r/Competitiveoverwatch/comments/763cnx/overwatch_league_and_confirmed_teams_so_far/
http://www.inven.co.kr/mobile/board/powerbbs.php?come_idx=4538&my=chu&p=1&l=3353113
https://www.reddit.com/r/Competitiveoverwatch/comments/76zwjp/all_owl_team_names_official_and_rumored/