Interesting debate....
I'll chime in a bit, if I may
I'll have both 31 & 43 and 50 and now I got FA*24.
Crowded? Yes, until you look at it as two line ups!
Heavy: 10-20 + 31 + 50/1.2 + 77 = all you want. Superwide, fast normal, ultrafast portrait/short tele, fast long portrait/mid tele. All in all, heavy and you need to rotate 4 lenses but you are covered for just about all people/vista/street/architecture/indoor shots...
On the move: FA24 + 43 + 77 (if you want) = compact, light weight. fast moderate wide, long fast normal, and fast mid tele.
Of course you can mix and match as you wish. But: I'll agree that 31 & 43 are too close. I'd never see 43 as cheaper option or downgrade to 31. They are both different and both have a lot going for them! 43 & 50? again, very close for comfort but far enough to keep both for different purposes IMO.
43 soft wide open? What a load of..... excuse my french... 43 is probably the sharpest out of all of these wide open (at least my copy is). Yes, it is bit softer in corners, but still OK. And stopped down it spanks everything else, almighty 31 and K50/1.2 including.
OOF? Well, down to personal taste IMO. I'd say it's good if you are careful what is in your background. On this occasion both 31 & 50/1.2 fare better, I'd even say quite a bit better...
A lot of folks miss one point though: hold your 31, your 50/1.2 or *55/1.4 and then grab 43! That lens is small, light, portable and delivers! And that is quite a winning combination IMO....
my 2p