Exactly why FCC (or the ROSCO) needs to look at a way to increase capacity of the existing stock, as extending platforms isn't an option. Opening up the currently private area (by doing it properly, not allowing some commuters to illegally occupy those spaces now) gives a lot of room. If that was left open, without seats, but grab handles and poles, you'd have a place for quite a lot of people to stand - which they could do for the busiest section of the line, before moving to a seat later on.
When I came home from Old Street and stayed on the train, by Hadley Wood the train was near empty. By Potters Bar, loads more piled out and by Hatfield it was very empty. I am not sure many people ever went from Moorgate or Old Street all the way to WGC (maybe 10 or 15 - and some of those would be people who actually boarded a lot further along).
If the seating was made 2+2, you'd get loads more people down the aisles, which would mean more people could move down and also get to the doors to alight quicker. I am certain that would make a real improvement, even though there would be more people made to stand. While some would moan, it's the lesser of two evils - and that's before reminding some commuters to try all of the doors and perhaps get on the train at the back...
At the end of the day, the franchise probably says they must provide nn seats per hour/day or whatever and that means keeping 3+2 and having little room to cope with the crowds. Imagine if such a rule existed on London Overground! Look at the transformation of LO after going from 3+2 313s to 378s. Proof, if proof was needed, that the current ageing stock could be modified to provide more room, which would hopefully drastically reduce dwell times too. You, better than most, know what it's like at Highbury & Islington! Thank goodness I was already in a seat by then...