Dedicated ammo for each weapon would probably make more sense in terms of realism. On the other hand, managing any type of munitions and stacking them up in the backpack is a tricky part. There is probably no ultimate solution for that. What I would attempt to do in such a case... probably the increase of stacking size of 7.62 from 150 to 240 is one of the solutions. Also, I would make sure that players as a reward may receive ammo type that can be chosen by themselves. Ammo could be less present in POIs, but instead, players might have wider access to it through trader somehow or a magic reward box/storage, etc. When it comes to a grenade launcher, it is a fun weapon to use, especially LMG bouncing grenades. In addition, the launcher might be attached to an assault tactical rifle or to be used separately. Flying AK is next on the list - just kidding. Without pain, there is no gain.
In addition to vehicle mods, I would like to see vehicles damaging or killing Zombies finally. Also, some XP granted for a confirmed Zombie kill would be cool, let's say 1/4 of XP for roadkill. Huuuge 4x4 truck for 4 or even 5 players inside. Such a vehicle could be customizable and a bit pricey, but might work as a mobile fortified base with .40 cal or rocket launcher during a horde night also. Sounds like lots of fun and more reasons to purchase/download or simply play the game, at least for me.
I believe that having 4 stiff classes, grand perks - you name it, with certain abilities and weapons behind it is actually a drawback in the production process. I would love to see weapons being developed independently from any list (so more weapons could be introduced for sake of content, same with abilities), perhaps as a separate tree for rifle and melee weapons, etc. So the pistol could behave finally as a basic/early game weapon and fists, with a low cost involved in perking these weapons, etc.
Then we could have some more like 8-10 smaller thematical clusters or trees instead of the 4-5 restraining lists that are currently present. Right now any change in Fortitude is automatically forcing devs and community to rethink the entire structure. I would rather break current classes into several categories developed independently from one another. This could grant wider freedom of choice to players at the same time. The main focus should be emphasized on the development of things, later implementation, balance, etc. Thanks to this solution in the early game I could perk in Stealth, and both Heavy and Light Armour at the same time with suppressed Pistol, etc. - why not. I hope that the devs won't give up on revising and updating the game.