Big ones for me:
Make Silver Hayes 4am
Build up/better advertisement of other late night areas.
Sort out SEC/Shangri-la bottlenecks
Electronic stuff is popular among the 25-35 crowd no doubt. But how many are willing to commit to DJs at headliner time (unless they're Bicep/Charlie sized) and stay out till 6 vs go with the flow, see a headliner, stop at the tent then back out for a dance. I think if the fest handles the latter you can reduce the crowds.
SEC is so out the way that you don't want to risk going somewhere else at 1am, potentially find it blocked off, then trek to SEC anyway.. This is especially true for the Pennards/Paines lot, Silver Hayes and SEC are essentially opposite directions. 4am is the sweet spot where everyone not on copious amounds of MDMA is probably happy to call it a night. Throw in some variety, maybe some basic or cheesy music stage to complement the DJs at Levels and boom, a viable alternative. Instead of everyone flocking SEC every night, most just choose one night.
I couldn't convince my group to go to Silver Hayes because it was just DJs so wasn't considered a 'must see' night time area, and they only time people wanted to go it was already full for Charli. Meanwhile, every day except Weds someone said "I really want to see Shangri-la at night (because they had gone to bed early or had only seen Block-9 so far).
The app is potentially a great tool, not just for advertising but maybe one day get to a place where they can say X is at % capacity. I had no idea Park had stuff running past 3 until reading this thread.
This year the SEC felt so chaotic. I liked Genosys, Mez Yard and Rocket Lounge, everything else worth seeing needed a lot of queuing. You end up with so many crowds walking through and bottlenecks. Iicon toilets were always super busy since they're pretty much in the way of the SEC entrance, plus the narrow entrance to Block-9, bit around Unfairground toilets was consistently uncomfortable. They need to find some way to funnel people through better
On another note, stuff like Glastobury by Sea and Healing fields are what makes the festival uniqle and I don't think the festival should pander to the sesh gremlins too much.