I echo Jake's sentiments, I think he'll get 15+ appearances. I know people probably think I overrate Januzaj, but I'm seriously more excited about him than I was with Pogba and I was excited with Pogba. The thing that sets him apart the most from Pogba is his attitude.
He's got everything in his locker to succeed. He's got the determination and hunger, you can see that just by watching the u21s matches. He's got skills as you've all seen this pre seasons, and he doesn't try to use them unnecessarily, he uses them when he sees an opening and knows when to play it simple. Which brings me to my next point, he's got maturity beyond his years and the type of maturity that I can't ever remember personally seeing from any 18 year old in the club.
At 18, you could argue that he's already too good for the reserves, he's the youngest in the team and the best by far IMO and I think he's too good to go out on loan as well. He'll do better just being part of the squad, training and getting matches when he can. It's not going to be an easy ride of course, and I wouldn't expect him to just walk into the first team, but he doesn't seem like someone not prepared to fight for it.
You can argue that he's played against weak opposition in this tour. But nevertheless, he hasn't just looked like he's fit in, he's actually stood out which is all you can ask for any youngster trying to impress.