Assuming equivalent UIs, what theoretical advantages to your third party off-chain service provide have that zero confirmation Bitcoin transactions don't already provide?
Privacy, and the best way to achieve that, chaum signatures, is inherently irreversible and instant as well.
Accepting this as true, for which you present a strong case in your thread on trusted banks, then this is indeed a complementary service which may well attract a significant user base in the future. It may even succeed in handling 90% of the transaction volume which would otherwise hit the main blockchain. Is that your optimistic scenario?
However, and correct me if I am wrong, but such a trusted banking service does not exist yet. Not even in a prototype form, let alone one that can rapidly substitute for blockchain transactions. Acceptance of new services like this will take some time, at least a few years, surely. The people on this forum are ahead of the masses on bitcoin usage, yet they universally appreciate that their holding is stored on thousands of nodes worldwide. How many of us would quickly and permanently move our bitcoin holding to one single service instead of having it stored directly on the main chain?
You use the word "trust", but it takes time to earn it. It has taken Bitcoin four years to earn the trust that is fueling its success today.
I argue that there is
not enough time left for that level of trust to be earned by complementary services before the 1MB arbitrary constant becomes as effective as any ddos attack in the history of bitcoin.
Please consider this chart and let us know, in your considered opinion, whether trusted banks will be fully ready, with a proven track record, before its blue line reaches 345,600.
https://blockchain.info/charts/n-transactions?showDataPoints=false&show_header=true&daysAverageString=7×pan=&scale=1&address=