It won't break the game to change it, but locking players in will make things a bit more difficult.
For instance, let's say the group accidentally pisses a bunch of people off, and for whatever reason, they don't want to actually fight - we'll say there's a business deal they want to go through. Initiative gets rolled, and we'll say 2 fighter PCs get to go, then 3 enemies, then 2 other PCs - a mechanic and then the group's face.
So if we lock in initiative, the fighters have two options, they take a chance and just start killing enemies, or they duck into cover and wait until the group's face can try and talk them down. Either way, the likely squishy mechanic and face are stuck sitting out in the open until their turns roll around. Fighters don't want them getting killed, so now they start fighting, and the face's chance to try and end things peacefully and keeping the deal from going south, plummet. Also, now the mechanic needs to wait until after the enemies have a chance to call for backup before he can try and seal the door.
You keep it how it is though, and you can let the face give calming them down a shot, and if that fails, the group can decide to either start killing or first try and block off the chance of more enemies.
Similarly, group decides to plan an ambush and they do Cool checks. Well, the face character is planning on just being backup while the two fighters jump the guy they plan to kill, but now he's stuck with the first slot, while the fighters how got bad rolls need to wait until they can actually attack the guy they were ambushing.