It is highly unlikely that arrow will appear in the justice league for multiple reasons, so let me list my top 5.
1. the green arrow isn't that well known.
if you said to someone who barely knows DC, name the members of the justice league, they will probably say Batman, Superman, Aquaman, Flash, Wonder woman and maybe cyborg or green lantern but the chance of them saying Arrow or someone like Shazam is very unlikely.
2. there already is a TV show
For someone who is a fan of Arrow and wants to see action, they watch the TV show considering its weekly and not every 3 years.
3. justice league are mean to him
they think he isn't good enough/hasn't got a power and can only shoot arrows, although, batman doesn't have a power....
4. there has been no casting for arrow
there hasn't been any known casting for a green arrow although there has for people like batman and wonder woman.
5. no stand alone movies
there is not going to be a stand alone movie anytime soon although people like cyborg has one.
let me know down below what you think.