Lanefan
Victoria Rules
With or without consultation with the other players/PCs?D&D's system of initiative was first introduced with AD&D, 1st Edition. Before that, many of the rules of combat were found in Chainmail, a set of rules for medieval miniature wargaming. The initiative system had evolved from the "Move/Counter Move" system of turn sequence found in those rules, but Chainmail also contained an alternative system for "Simultaneous Movement". It is from this that the following has been adapted for 5th Edition.
Simultaneous Initiative
1. When combat starts, every participant writes orders for the character or monster (or group of identical creatures) they control, including direction of movement and action to be taken.
If you don't allow consultation and have orders written mostly in secret this could work quite well and nicely provide a fog-of-war effect. Allowing them to consult before each round gives them far too much of an advantage of synergy IMO.
If after the first half of someone's actions etc. gets resolved the second half no longer makes sense, can the second half be changed or is the PC committed no matter what?2. Every participant takes up to one-half their movement and any actions they can take according to their written orders, checking for opportunity attacks and other reactions due to movement. Conflicting movement and actions are resolved with contested Dexterity checks. Participants who are targeted with a melee attack and haven’t already used their action may use their action to make a melee attack in return after the triggering attack. Then the remainder of movement and remaining actions are completed as ordered, with conflicts resolved and melee attacks returned as above.
This has always been my issue with pre-declararion of actions; that sometimes a pre-declared action doesn't make sense by the time the PC gets to do it. Example: I declare that my archer this round is going to move to point X and then take a shot at opponent Y. First half: I move to point X and get ready to shoot, but meanwhile someone else slays opponent Y. My intended shot for the second half is now pointless unless I'm allowed to retarget.
The issue would go away here were you to make each "half" its own new round.