This opinion may be unpopular but I don't think mimikyu should be banned.
Reasons
1. A ton of new pokemon learn both Taunt and Encore beating mimikyu's main set (Curse, Endure, Phantom Force, Substitute, with Custap Berry or the slightly less optimal sets with Sitrus/Salac. You may disagree with the best sets, I'm just biased because I made the Custap set).
2. Many pokemon beat Mimikyu's Curse set if they have Yawn, Trick, Recovery moves, Leech Seed, Salt Cure, Multi-hit moves, Mold Breaker, Priority Moves, Faster Normal types with a non attacking move (50/50 with predict), Gholdengo, Burn, Poison, chances with Para/Sleep, Some Berries, etc. These are some more obscure move choices, but with such a wide variety of move choices it is likely you can fit it on your team.
For example, a Weakness Policy Chi-Yu with Will-O-Wisp. (This set could be bad, it's just an example)
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Problems
1. You still don't know if it's an offensive mimikyu or Curse. This causes problems because pokemon like Iron Bundle who beat Curse lose to the offensive set. But isn't that just normal 1v1? Many pokemon have several different sets beating specific mons.
2. The Custap set on mimikyu is problematic because it was never used in older generations. Normally fast mons would always beat mimikyu (if they are faster than +1 from salac, which many are in this gen), but with mimikyu you are guaranteed the win against any pokemon without encore/taunt/the moves listed above.
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Examples of how to play mimikyu (many would lose the mu shown below even though it is winning)
Flutter Mane vs Mimikyu (Ignore that phantom force would probably just ohko)
example: [t1 Moon Blast, Curse] [t2 Calm Mind, Endure] [t3 Moon Blast, Endure] Mimikyu has a 50/50 chance of surviving here if they get to Endure or if you predict the Calm Mind.
example 2: [t1 Moon Blast, Substitute] [t2 Moon Blast, Curse] [t3 (Custap) Phantom Force, Moon Blast (miss)] [t4 Moon Blast (miss), Phantom Force] [t5, Moon blast, Endure] In this example the faster mon just loses with no chance to win unless they are a normal type or if they heal more than the damage dealt by Phantom Force via berry/leftovers.
But this sounds similar to what other pokemon can do. Dig Riolu loses to EQ (if they are banded he learns magnet rise), and Whimsicott loses if you can 1 shot it/have a multi-hit move, etc. (and there are berries halving damage). There are plenty of cases where only specific moves or types of moves can defeat pokemon.
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Conclusion
While mimikyu is a serious threat, this generation has been given many more options to beat it than any other generation. I tried to address the problem and weaknesses of mimikyu equally and gave out information that many probably don't know on how mimikyu can beat even more mons. I could have left this out to show only the weaknesses, but I tried my best to instead share everything I had.
As the meta develops we will see what has to come, but I do not think mimikyu should be banned any time soon. A very similar example to this is Zygarde Complete in generation 8. It took a very very long time to ban his ability even though a team was considered bad if it did not have a counter to him. It probably had 4 different sets and each one was viable and could beat different things.
If you do decide to ban mimikyu I would like you to consider instead banning move combinations or specific items with it (like how Magnet Rise and the Electric Z move are banned because it raises evasion or Leppa berry with Recycle and Heal Pulse. These are banned because they break the endless battle clause and evasion clause, but still relevant I think).