Like I said before it's not that you can't beat sleep, it's that it will make the metagame dramatically different and that might not appeal to certain players. For instance, Scarf darkrai becoming the top notch scarfer because of its ability to buy time against pretty much every threat not running lum berry, and any arceus form lacking sleep talk bar extreme killer, or the simple inability to revenge its usual sweeping set with a scarfer could be extremely troublesome. You mention beating darkrai with a scarfer, but to get in safely with no sleep clause, you have to make a pretty massive prediction. We can all run scarf heracross I guess, but logic like that was used to keep things out in OU testing.
I think that sleep talk will be the most similar to OU testing out of all of the options, simply because we do have most of the tools to deal with the main abusers, and it will retain the most elements of player skill. Specially defensive Kyogre is and will always be an excellent sleep absorber, and is more viable than ever with kyu-w running around. 50/50s will certainly abound when we test sleep clause, but smart teambuilding can certainly manage risk here.
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