It took me a while to start writing again, but here we are!
Here is a list of current backup goalkeepers who might end up being a number 1 next season or maybe earlier.
The Dutch goalkeeper from PSV lost his spot already last season to Mvogo. With the arrival of Benitez it was clear immediately Drommel would be the backup this season.
Drommel arrived from Twente last season where he performed very well and therefore really gained his transfer to a better club and even made it to the national squad of Holland. With Anderlecht already interested last summer, it would be weird that Drommel actually stays another full season in Eindhoven for the season 23-24, time for him to be number 1 again somewhere.
The French goalkeeper is playing for Monaco this season as the backup for Nübel. It looks like Nübel will not move to Bayern, so for sure, he will remain number 2 this season. Even if Nübel would move after all, I do expect Monaco to get another goalkeeper (it does look like Sommer will make the move to Bayern). Monaco is the owner of the Belgian side Cercle, where Didillon was number 1 last season. He always indicated he wanted to play for Monaco, but staying another season as number 2 would be strange. Does he go back to Cercle and Majecki (on loan at Cercle from Monaco) does the opposite, who knows?
The Spanish goalkeeper is currently at the newly promoted la Liga team Almeria. After playing a full season for Alaves, who relegated last season, several teams were after Pacheco to sign him. Although they were relegated, he played a very solid season for Alaves. In Almeria, he expected to be number 1, but Fernandez who won the promotion with the Andalusian team, kept his spot. There are already some rumours around Pacheco, mainly from Espanyol and Real Madrid, the first one would be to battle for 1st spot against Lecomte and Fernandez; Real Madrid is of course as a backup for Courtois, assuming Lunin will make a move.
The Swiss goalkeeper plays for Celtic. He is already playing in Scotland for a while now and moved to Glasgow after some successful seasons at Dundee United. During the summer he was rumoured in different clubs, mainly in the English Championship, but he moved to Celtic after all. With Joe Hart there, he also knew he would be number 2 in the beginning. The question is how long does Siegrist see himself being the backup goalie? This season would make sense, and with Hart starting to be a bit older, does he hope to become number 1 next season? Or if not, wouldn't he want to move somewhere else to be the starting goalkeeper again?
Playing for Club Brugge, Lammens is the backup for Mignolet, and let's be honest, that's going to be difficult to become number 1. Lammens is a huge talent and is number 2 for the Belgian U-21 squad behind Vandevoordt. Lammens is out of contract next summer and the media indicated he wouldn't renew his contract. He did play some matches for Club Brugge B (Club nxt) in the Belgian second division, so he could prove himself already. If he doesn't want to renew and be the backup at a top club in Belgium, I might assume he wants to become number 1 somewhere.
Horn is playing for German team 1.FC Köln. And we can say he is a club legend, after playing around 300 matches and being in the club since 2002. Since he was injured last season for more than a month, he lost his spot to Schwabe. This season he wanted to battle against him for that same spot but the manager kept his cponfidence in his competitor. Out of contract this summer, does he remain with his club or is it time to move on and choose for his career to become number 1 again somewhere? I would think it's the second one and seeing him in a low-tier Bundesliga team or high-tier Bundesliga 2 would make sense.
The Albanian goalie currently plays for Premier League team Brentford, where he is the backup for David Raya. Out of contract last summer many rumours were around him, mainly from the premier league teams Fulham and Brentford. Signing for Brentford seemed a risk as Raya did play well last season and even made it to the Spanish national team as their 3rd gk. Since he didn't play any league match since his arrival, his agent already communicated it might be time to leave again, unless something happens with Raya and he makes a move, as very recently Ajax was interested. (but Ajax seems to have chosen Rulli as their new gk)