Well, it was clear that they would have to play 50+ games this season to complete all their (self-set) goals.
If you check the early games of this season, before it started raining injuries and Piszcek was the only wheelchair candidate, they already had mostly 3, sometimes 4 players from their reserve squad as substitutes on the bench: Durm, Hofmann, Günter, Kirch...
Add to that Schieber who also is no adequate substitute for Lewa.
Some of the young lads are undoubtedly very talented, but not there yet. Also i wonder what good it will do to the development of those players with the huge weight they have to lift at the moment.
No one is talking about summing up a bench like Bayern. But there is a way in between those two extremas.
Well, Klopp thought differently and given his track record with the development of young players I know who I would put my money on.
Ideally the bench for the first season half would have looked like that:
Langerak - Sokratis - Durm - Kehl - Sahin - Aubameyang - Schieber
Jonas Hofmann would be the first offensive player in line to move in and either Sarr or Kirch being the first defensive counter part.
The only player in that list, which could be called a reserve team player is Marian Sarr, because he is the only one to actually have frequently played in the second team in that season.
Hofmann and Durm are NOT reserve team players, unless you call them like that because they moved up the ranks, which makes no difference because in the end the quality decides and not from where they come from. They made enough impressions for Klopp to put their trust in them. As a result both received first team contracts and a place in the squad. They are squad players and this is not erased because of their young age, although 21 is not even that young anymore in the current Bundesliga. They also proved Klopp right.
Durm was pretty much always there when needed and aside from a few inconsistencies plays an absolute fine season so far. As logical consequence he became a German U21 International.
The same status was archived by Jonas Hofmann, a player who would probably start in half of the Bundesliga teams. Hofmann did extremely well as impact sub (he was originally only the 6th option in the offensive midfield afterall), scoring two goals and seven assists in the 390 minutes he played for Dortmund this season. This is a quota that most squad players can only dream of.
So yes, Klopp trusted some of his talents to carry some weight just like he has always done in his career as coach. It carries some risks but not doing so and only going for finished articles will probably never happen in Dortmund in the near future, because it is simply not Klopp´s way (the way this team was built in the first place) and would negate one of his greatest strengths as coach: his ability to develop talents.
It is also not part of the current problems because the talents had the wished development. The problem is the extreme concentration of injuries in the defense, which can´t be solved unless they increase their wage bill by a large amount. Otherwise you won´t get quality players (numbers alone won´t logically help them) who will happily sit on the bench and wait for the current highly unlikely scenario of having the whole back line and CM wiped clean to actually get game time. For players Borussia Dortmund is not a club to become rich by sitting on the sidelines, but to actually get some perspective to make an impact.