Nice write-up. Jealous of your dreams. I'm by no means an expect on these matters, but anything that requires miners making a decision is probably best avoided.
I believe the solution to the problem is effectively what Payjoin offers. Without any hard fork or soft fork required. Using pure business and financial incentive to scale. We just need to accelerate its awareness & adoption.

What is Payjoin? If you're still unsure of how Payjoins work, here on SN is perhaps the best write-up of late from @ratiotile, then there is the site or my SN teaser.
Payjoin incenitivises any exchange, wallet, lightning-btc swap service or any business whatsoever to adopt collaborative transactions. Privacy isn't even really on the agenda, because not only can it help the business save on fees, it can cut-out entire transactions entirely by connecting buyer with seller, customer with supplier or multiple parties with multiple parties.
Rather than going from A) customer to B) company to C) supplier. B could just accept payments that automatically forward all A) customer deposits to C) supplier addresses at a given interval/period.
There's no miner incentive in this case, in fact it will reduce their fees due to a smaller chain footprint with fewer transactions. Yet that's probably something to be celebrated, there is no decision for miners to make.