Coding the game in such a way that a gun's rate of fire is dictated by client-side FPS
This is pretty common in a lot of games, but we fixed this in PUBG over a year ago.
https://www.pubg.com/en-us/2019/02/20/test-server-update-26/
Adding in-transit healing which may be canceled by vehicle movement.
This was an intentional balance consideration when we first introduced healing in vehicles, but you're right, we should look at changing this now that players can move and heal. F to suicide is an issue, for sure.
Requiring professional players to rename their accounts without providing the ability to--nor preemptively deciding to--reserve their old names causing them to be impersonated by random malicious actors who took them
I don't have the relevant background on this to respond to the specific instance you're referring to, but I don't believe we require any pros to change their names on live servers as they use dedicated clients for pro games. If anyone changes their name on live servers it will eventually be released for use by other players.
Pushing every single update in an unchanged form, no matter how negatively it has proven to impact the game on the test servers
Somewhat of a fair comment, but if you look up the updated notes for 7.1 we have made three additional updates to this from when it was on live server, and this can be found in a lot of updates, but I assume you're referring more to gameplay changes which are disliked by some of the community.
Finally adding a 'practice' mode where players can practice shooting.. in multiplayer.. with. unlimited. crossbow. bolts. and. stun. grenades. and. smokes. and. molotovs. that. make. you. unable. to. practice. you. can't. make. this. sh*t. up.
Smokes and stuns were removed in week one of training mode being added. Remaining from the throwables are grenades and molotovs.
https://www.pubg.com/2018/09/05/pc-1-0-update-21/
If you have more suggestions for what can be changed to make Training Mode better I'm happy to talk about that and bring it to our internal discussions. :)