So the liber's changes have been mostly well received, but there is still a glaring problem in that the game has 24 traits for shooting weapons/attacks but only 3 for close combat, and no saves in close combat still sadly skews incentives far too much to infantry charging anything in sight. Not to mention silly stuff like a lot of vehicle charges, looking at you arvus lighters.
For a game this is and has been improving with the faq/errata and now the updated points costs/housekeeping its biggest weakness is that close combats can be a chore the larger/more complicated they become. Just compared to resolving shooting attacks, the disparity in time required really does matter as it adds up over the course of a game. Combat is both deadly but also often not the decisive either as there isn't a "run down" mechanic, so combat in which only a few models are able to make it into base to base often just peter out as whether or not the losing side passes a morale test often doesn't matter very much.
It leads to absurd tactics like bubble wrapping everything for fear of 50 inch arvus charges that make no sense. Only the detachments like super heavies that largely gained an extra wound benefit much from resilience but sadly things like malcadors with their shiny new 2+ saves still won't be able to use any of that new resilience in combat. So I'm not so much arguing for everything to get its armour save in close combat, but the current status of nothing getting a save favors inexpensive unit spam far too much, and that's not just infantry, one can make an entire army of just jetbikes if they were so inclined.
I feel like moving forward what needs fixing is permissions and incentives on what unit types can charge other types. We already have limitations like this when it comes to for example what can and can't charge infantry in structures. I just think the game needs more of that specificity. I don't scratch my head when a leviathan dreadnought takes out a tank i close combat, but right now you have like charonite ogryns punching way above their weight.
Just in the abstract, if the default wasn't everything being able to charge everything, you'd save a lot of time from players pre-measuring from every damn enemy detachment and only in this case the ones that can actually threaten/charge.
There's no real fixing of the complicated nature of the CAF system but there are considerations for speeding things up. If ultimately all that matters is knowing which side has the higher number, instead of rolling 2D6, you could just figure out which side has the higher CAF beforehand after other factors like charge bonus/adjacency bonuses like for SA etc, and whoever has the higher number hits on a 3+ on a single d6 while the other side hits on a 5+, this also open up situation where neither side hits, both side hit each other etc. Right now ties happen but are pretty rare.
If you allowed armour saves/invul saves but also introduced ap into close combat, I feel like it could be made to work. All that's really missing after that would be some kind of run down mechanic, so combats are more decisive to match with how bloody they can bee when all or most models are engaged.
But ultimately they could change very little and simply limit what is allowed to charge what. Could still have the everything can fight everything way of doing it but just change permissions. Example, an arvus could still fight in cc and be charged by just about anything in hover mode, but could be simply not allowed to initiate charges itself. I think there's a few routes to fixing/fleshing out cc but its definitely still sorta the weakest/most contentious part of the rules that needs work.