I asked for an example. Saying what the result is without having a good example for where the power definitely gains something real doesn't mean anything. For what At Will does this significantly matter where End of Your Next Turn wouldn't work just as well?
For example:
Devastating Strike. The difference between Start of Your Next Turn and End of Your Next turn means that if you provoke an OA (a relatively rare occurrence which player controls) against the foe and if you are not raging, the foe gets +2 to the hit roll which means that maybe 10% of the time * 10% of the time or probably less than 1% of the time, this could actually matter.
Is a 1% difference in outcome worth it when compared to simplifying the rules? Not in my book.
The movement inhibitors would shut down a lot of reactive movement abilities, and some feats and abilities trigger off of status effects: Net Snare, Iron Soul Flurry of Blows, etc.
Aura and zone abilities could be more easily abused in conjunction with movement powers, and you could even have TWO of them up at the same time in the right circumstances: Ignition, Rotting Doom, Body Double, etc.
Special combos can crop up where you can use one ability to magnify another: Karmic Bond+Unconscious Assault, Paint the Bulls-Eye+Direct the Strike, etc.
Abilities that start creating a stacking loop that amplifies the effect: Memory Hole/Eyebite, Playful Torment, Brash Strike, etc.
These are also examples of why action points are so powerful - you can layer abilities in ways normally unavailable.
And please note, that's JUST At-Will powers. The combos you can do with Encounter and Daily powers can get nuts. I also ignored anything to do with OAs, since that can be more game-dependent and you don't consider them valid arguments anyway - which means you chose Devastating Strike as a strawman argument.
Also also keep in mind that this includes not only current powers, but hypothetical powers. In fact, the whole point of this is that 5E's powers will have to be more limited than 4E's powers if this happens, if it's to maintain anything resembling balance.
It only typically allows you to double dip if you are using an Action Point. For example, Blistering Flourish. If this power wasn't until end of your next turn, it wouldn't do anything above a melee basic.
You can triple-dip if you include action points, actually.
Ardent Outrage, for example, could trigger from an OA or other damage at the start of your turn, after which you could make an attack. With an action point, you'd get two extra standard actions to utilize that effect. You'd also have a chance of getting some boosts between your turns.
And, there are a ton of powers where there is no such thing as double dipping. Burden of Earth only allows a single +1 bonus. Shield Feint only allows a single +3 bonus.
Yes. They'd get an increase in power here, too, and could be combined with whatever you use on your next turn to give a target a double-whammy, say with a to-hit bonus AND a damage bonus instead of just one or the other.
Or, powers that allow double dipping, but it requires subpar play. For example, Vicious Mockery is a debuff, so the only way to double dip it is to provoke an OA with it. Hardly something worth discussing.
Funny how all of your examples are things you consider not worth discussing... Come on, guy. Just say "I do not consider OAs to be worth tactical consideration." and then talk about things that do not involve OAs so we can have a real discussion.
A lot of "until the start of your next turn" is actually for whether something happens, not for a buff or debuff or nasty effect for that duration. For example, Escalating Violence. And like the Devastating Strike example above, the Barbarian would have to provoke an OA if EV was an end of your next turn power in order to get a slight bonus to hit and damage. Sure, it would be an option, but hardly game breaking.
Can you give an example of a throttle back with this?
See above.
It's not important at all. Until the end of your next turn is a superset of end of target's next turn and also ensures that the effect WILL affect the target, so this option isn't needed. It has no significant gain.
Unless you have an example where end of target's next turn is balanced and end of your next turn isn't.
"End of your next turn" allows you to take advantage of something directly.
"End of your target's next turn." only allows you to take advantage of something passively unless you use an action point.
Ardent Strike would outright suck if it was "End of your target's next turn." unless initiative order was just so, and "Erupting Flare" wouldn't force enemies to flee to protect their allies if it was "End of your next turn." because those allies would be able to flee on their own.
There really is no need for 4 different types of partial round durations. One is sufficient.
No durations at all ever is also good. Conditional durations is also good. There is no magic number, but I far prefer mine to yours, as it allows for more possibilities, but isn't as complex as conditional durations. And someone out there would just LOVE conditional duration D&D.