I believe having a reserve team feature in career modes like player an manager will benefit the user experience. I believe if the feature was included in 'Be a Pro' this will improve the experience by allowing yo to start off as a youth/reserve player, the playing in fixture like the next generation series( I believe this should be included because it was such a hit.) For example of this, you can start of as Lewis baker/ Billy Clifford and then play fixtures against other team reserves/ under 21 like Arsenal. Also play in the next gen with reserves from around Europe. This feature can also take place in 'manager mode' where you can select players to include in the tournament also you can have he ability to play the fixtures like 'international manager' which was introduced in FIFA 13.
I believe this feature has been missed since not being included since FIFA 09. This is a feature where I was missing and was so passionate about that I was going to inform the public. I hope this feature will be included which WILL benefit the user experience.