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as for spam attack bitcoin.
easy solution.. implement a fee priority.
instead of everyone bidding for top price. have a formulae where if your spending funds with less than X confirms you pay more then someone who has XXX confirms.
that way spammers that need to spend multiple times a day pay the price.. or use LN for its niche. and those that use bitcoin irregularly are not forced to use LN and not forced to pay the same price as a spammer.. win win for everyone
so far spammers have never done it on a tiny scale or for a short time. they have always done it over a very long period of time (a couple of months at least) and on a very large scale (as in using thousands of addresses). they even started hiding it in 2017 well enough by running a "warm up step" first where these outputs first spread to the appropriate addresses then those addresses start spamming and after the spam was done they all aggregated again.
in other words your suggestion will only screw normal users, the spammers just have to run a "warm up step" where they spread their outputs sooner and on a larger scale to have enough confirmation on them to pay less fees.
on top of that they have proven that they don't have much of an issue with high fees, possibly even have miner ties which makes it cost a lot less for them to spam (they get the fees themselves on blocks they mine)