Just had a thought....
The A321 wing area is 122.4 sqm, the flap area is 21.1 sqm and the flaps have a span of ~0.78 of the overall wing span. Which works out at an average chord (not MAC) of around 0.8m.
- the flap track were adjusted such that the first 20% of aft travel were at 0 deg angle of attack
- the spoilers could depress slightly below 0 deg (they already will to an extent for prebow effects)
- Additional shrouds were added to the wing pressure surface (which can be translated forward for conventional flap functionality)
Then overall wing area could be increased by perhaps around 3-3.5% - without carrying that added wetted area when it is of no use
The A320 flap track mechanism is the right images in ; the flap (i) translates down the golden track and (ii) pivots as a result of the rotary action of the flap track motor. The track could be reprofiled (non-straight) to achieve the same max deployment angle (but adjusting intermediate angles) without massive upheaval in the mechanism.
Looking further down the road, completely decoupling aft translation of the flap and rotation of the flap could leave you able to expand wing area by maybe up to 60% of the flap area. In the case of the A320, that would be over 10%!
Again, that would be an extension in wing area that is a pilot deployed option. Are you flying 4000nm at MTOW? Want to get to 40kft quicker? Expand the wing. Are you flying 500nm at weight well below MTOW, then minimise the wing to reduce wetted area.
There would be a weight penalty to the more complex mechanism of course, but its likely on the order of tens of kilos. But your wing loading might drop from (@ TOW 101Tonnes) from ~825 kg/sqm to ~750 kg/sqm. To me, that's worth carrying 100 kg of extra mechanisms.
Might be something we see in the future.
 https://booksite.elsevier.com/978034074 ... /table.htm
 https://upload.wikimedia.org/wikipedia/ ... 7_A320.png
 https://theflyingengineer.files.wordpre ... 1/11/n.jpg