I am aware of the crucible online but noticed that on the Login to the master vault you can use your PS4, Xbox, Steam or Nintendo accounts.

Is this an indication that we might be getting something legit in the future? The crucible online is good considering, but find it problematic and unasethetic at times.

FFG is a part of Asmodee, who has a pretty decent catalog of games for various platforms (Steam, Switch, PS, etc.). Since the Master Vault uses your Asmodee login, you can associate your other accounts to your Asmodee profile there.

Will there be official online play? Probably.
Is the fact that your account can link to other platforms an indication it's coming soon? No, it's just part of the larger Asmodee ecosystem.