IMHO, when/if Bitcoin gets mass adopted we'll see most of it being transacted on layers 2 and the first layer will be used by computers, companies or apps rather than individuals. First we need the experience to be user-friendly, cheap, fast and reliable. All of this can be achieved with more centralized systems that rely on the decentralized blockchain. And even decentralized ones, of course. I can easily see LN and maybe other, new, successful networks using BTC in its core but interceding between the blockchain and the average joe. So, yes, my answer is more than 50% of it.
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I guess one other consideration I should have thought about is the fees for confirming a BTC transaction in a decade.
My guess could be way too low if fees get extremely high on the Bitcoin blockchain.
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