Usually, there are 8 spots for midfield / wide forward player types in our matchday squads - 5 to start on the pitch, and another 3 on the bench. In general, the other 4 bench spots go to a centre forward, 2 defenders and the keeper. We currently have about 12 players vying for those 8 spots:
CM: Gerrard, Henderson, Allen, Lucas, Can
CM / AM / WF: Sterling, Coutinho, Lallana, Markovic, Suso, Ibe, Teixeira
I think Teixeira will likely go on loan, given the lack of minutes he's been given in the pre-season, which leaves us with 11 guys. Barring injuries and suspensions, the 5 in bold are certainties to get into the matchday squad, with the other 6 battling out for the last 3 spots every week. If Ibe is to get 15 or 20 games this season with significant minutes, he'll really need to shine in training to emerge from that pool, given that Allen and Lucas have the advantage of experience and familiarity with the league, while Suso and Can have the benefits of having a season of senior minutes under their belt in their development.
I'd still go with the idea that Ibe should stay with the squad for the first half of the season, to train with the club and get some minutes in our games. We can then decide in December whether to keep him for the rest of the season or send him out on loan to further his development in the second half of the season. Probably applies to Suso and Markovic (despite his price tag) as well. From the pre-season, Can certainly looks the most ready of the 21 and under players in that pool.