If I read correctly, there is no surprise anymore (granting advantage or disadvantage on initiative isn't surprise, IMO).
So, no ambushes where one side acts first. No planning what to do outside a door, opening it, and acting first *
Is that correct? If so, not a fan....
*sure, you could theoretically let your players ready an action for opening the door, but that's just gaming the system, IMO. Otherwise, why not let them walk down every hallway, with actions always at the ready? They would always get to go first every fight....
I'm likely going to not play by this particular rule (and it is another example of why I hate the initiative rules in 5e).
I get that this rule is made to make surprise less powerful. I want surprise to be more powerful. I don't mind a group engaging with the world to get a significant advantage. Combat isn't the point of play, I don't mind a fight where one side gets a little stomped, or where the PC's need to seriously evaluate whether or not to run because they were caught off guard.
If I do a "surprise round" (which is easy and straightforward and so might be what happens) or even just a "surprise turn" (one person gets to go before we roll initiative with 2024 rules - a less dramatic change with some impact), then what I'll want to do is make ambush rules very clear.
For PC's
If you want to ambush the enemy, describe how you set up the ambush. The DM will ask for checks depending on this description (typically Stealth for hiding, but perhaps Deception for luring someone away from their post, or even Investigation to find a good hiding spot). We'll use the 2024 rule of thumb of DC 15, and we'll make it a group check - if half or more of the party succeeds, the check overall is successful (so it's OK if your paladin just tries to lay down and not make a noise, the check can accommodate one failure). The monsters will make passive opposing checks depending on the skills the party used (typically Perception, but maybe Insight, or Investigation, or something else), also with that DC 15 as a rule of thumb, and also has a group check (so not every kobold needs to see you hiding, and we don't let one nat 20 ruin the whole attempt). These passive checks can turn active if the enemies have some reason to be suspicious (so a better plan means less chance of high rolls determining surprise)
If you succeed on your checks and the enemies fail theirs, you get a surprise turn. It's up to you who takes that turn. After that turn, we roll initiative, and you have surprise - you have advantage on initiative, and your opponents have disadvantage on initiative.
If you succeed on your checks and the enemies succeed on theirs, the enemies are aware enough of the ambush that they roll initiative normally. You can still have advantage on your initiative. You don't get a surprise turn.
If you fail on your checks and the enemies succeed on theirs, everyone rolls initiative normally - you didn't set up a successful ambush, they knew you were there. You don't get a surprise turn.
If you fail on your checks and the enemies fail on their checks, you roll normally and the enemies roll with disadvantage. You didn't get the drop, but your foes weren't really aware of you until the attack was sprung, either. You don't get a surprise turn.
For Monsters.
If monsters want to set up an ambush, they'll do basically the same thing - make group skill checks depending on the nature of the ambush, DC 15. PCs will have passive opposing checks, also DC 15 (and these can be actives if they're suspicious or otherwise keyed up). Same range of results between surprise turn + advantage + disadvantage to "everyone does initiative normally."
This is off the top of my dome, so I'm sure there's nuances that I might want to check, but I'm fond of the idea of being close enough to 2024 that it won't skew the expectations, but making an attempt at gaining surprise a bit more impactful than it is by RAW.