Heres a couple of things I would like to see in GHB 2 just my ideas but they've all be discussed a club a one time or the other.
1 Measure base to base seems to be pretty fairly widely accepted already.
2 Command traits and artifacts, spells etc for factions with books that don't already have them eg Stormcast, Bloodbound etc
3 Some points re-balancing putting OP stuff up and under preforming stuff down will mean tournaments scene stays fresh, as new options open up and other list become less viable.
4 More Allegiance specific battle-line so people can play more themed armies
5 Maybe 6 new scenarios the old ones are fine but a few more options would add some variety.
6 Maybe a base size guide nothing too restrictive/indepth but just a guide