Cooler is a non-canon element and with the mistakes they made in his movies e.g. Gohan having mushroom hair and a tail. And in the next it's either before or after androids so either Goku should be sick or Vegeta having SSJ shouldn't be known.
He cannot exist in the cannon timeline.
No news on who the villain is. I doubt it's the Cooler we all know from M5 and M6.
If they decide to bring Freeza's bigger brother, I'm fairly sure they'll create a completely new brother.
I hope he does not make an appearance. While I did love Cooler, I don't think it's right for him to return to something that could potentially be canon. I want to see brand new fresh villains.
It would be cool if he returned in the series, thus confirming the movies as "another universe". He'd still be alive and maybe not in a super big role.
Can't say I see Cooler coming back as a main villain. Some sort of acknowledgement to his existence however does seem entirely possible. A quick cameo or mention seems most likely, if anything is going to happen.