We do need some good back-up. Last week we had a very young keeper on the bench because Jones was injured. We also need a reserve keeper who is genuinely ready for matches. I know it's a different set-up these days but I still think a reserve keeper should be a regular part of the reserve squad as well as the first team squad. The reserves don't play that many matches, and there isn't an overlap in terms of fixtures, so I don't see why the number two shouldn't figure in, say, a quarter to a third of reserve games. That would at least give them a few competitive games, and it might help the younger keepers to watch and work with a senior pro (I know they already do in general training, but match day preparations would also help).
As for Mignolet, well, this is probably an irrational prejudice of mine, because I don't know what goes on in sessions at Melwood, but Achterberg doesn't seem a great goalkeeping coach. Nice bloke, but, since he arrived, Reina declined in terms of fitness and form, and Mignolet, as this thread suggests, has been struggling to cut out some bad habits. Hopefully we're looking to improve that area - Rodgers hasn't been reluctant to replace several coaches, so presumably he's open to another change there.