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As I have written in the reply to niftynei, "In my mind what makes a layer is the number of participating entities". So yes, if Kraken, River and some other exchanges allow users to pay each other via LN, then I'd say they form an L3.
I object to calling WBTC L2 because there's only one BitGo, but if there would be 100 different custodians I'd say they form an L2.
Ok. I don't consider the number of trusted third parties involved to be what distinguishes between what is and isn't a distinct "layer" on bitcoin but to each their own!
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