It would be nice to be able to remove certain single irons from your bag from your iron set, and replace them with other clubs.
A management of the single club for all clubs would be really great, so you could really fully customize your bag.
This way you could put on the pro shop some single 2-Iron or 1-iron clubs to fill the gap between the 3-Iron and the 3W, and tick off the 4 Iron or the 3 Iron (or what else you think you don't need).
Or even remove the PW and/or 9-Iron and use more wedges.
The best would be to be able to buy every single club in the range 1-Iron through PW.
For the existing sets, you could sell the 3I-PW set at that price, and the single clubs at a slightly higher price.
This would even allow for more special "Loft" clubs or "Shankless" woods.