I think there could be broadly two possible directions:-
1. If the meta aims to become balanced, continue with fast and heavy quickbans. This strategy might take more than one month to succeed, but I believe it eventually will, since many abilities have inherently limited value or potential synergy and are difficult to combine into broken combos (e.g. Inner Focus, Keen Eye, Frisk).
I would anticipate that almost abilities that give passive multiplier to stats or damage output would be banned in this scenario because they have dangerous synergy when stacked and are too asymmetrical between attack and defense to check each other properly. E.g. people are currently arguing for abilities like Fur Coat to be kept, presumably to deal with offensive abilities like Adaptability, even though the offensive equivalent to Fur Coat (Huge/Pure Power) is already banned; abilities like Adaptability and Tough Claws don't have direct defensive equivalents. Even if the offensive and defensive boosts were symmetric, there's something overcentralising - and arguably quite wasteful and boring - about dedicating a part of each team just to keep up with stat multiplier races. Removing these categories of abilities completely seems like the likely stable end result of bans without accepting broken-checks-broken.
Many players probably would not enjoy this outcome, since the long banlist would harm accessibility, and (a perhaps larger perceived problem) the meta could not deliver on the "dream" of using ridiculous broken combos like steel spam. However, I don't think realistically this and balance can co-exist; the power inherent in the OM mechanic is so large as to make abilities that would typically be reasonable in metas like AAA or Inheritance spiral out of control.
2. Give up on balance and embrace the "fun" brokenness. Unban most things that don't result in technical problems like Regenerator++Emergency Exit (as for Harvest, I don't understand why the Leppa Berry example wasn't eventually triggering Endless Battle Clause...?)
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Regardless of whether balancing is considered insoluble, I don't think it's necessarily a fundamental problem, and I'm very glad that this meta was brought back. There's even something quite interesting and compelling about the 'ban of the day' phenomenon itself, as in some sense it keeps the meta continually fresh - I feel like this probably contributed to SP maintaining popularity throughout the month in Gen 7, and it might well be the case again.
This seems unlikely to be considered. Firstly, OMs in general seem to be moving away from allowing 'restricted' item lists (e.g. AAA had Restricted Abilities removed this gen because it was considered a complex ban, even though the system was demonstrably functional during Gen 7).
More importantly, this approach was
tried and shown to be insufficient to quickly stabilize SP in Gen 7 (Mold Breaker specifically was restricted and continued to cause problems until the meta itself was banned). It just adds even more complexity to the balancing debate and gives abilities that really need to be banned a place to 'hide' while still being stackable with almost every other ability.