You can't cause a big queue of ships because you want to regulate and charge for passage even when you change the Montreux Convention. You need to create enough capacity for ships to pass through without causing bottlenecks. Given the impending huge cruise ship business coming to Istanbul with Galata Port there will be additional blockage of maneuvering ships which can decrease the passage capacity of Bosphorus.
As you can see from the Suez Canal incident that a ship can be made to block a Canal at critical times causing the system to fail with many consequences. Another Canal passing through Israel territory is being proposed to enable "continuous traffic". You probably remember Independenta incident as well. Bosphorus with its fast moving waters is passage that is inherently unsafe for shipping and for the city hosting it. Status-quo can not enforce even pilotage for passage.
This is a bet on the bright future of Turkey; those who bet Turkey will be wealthier want the canal, those who bet otherwise stand against it. Turkey will not settle with a single lane passage to wealth.
Why would charging cause a que? Payments go automatically by bank transfers, all ships who want a passage transfer beforehand the fee, it is not like a gate where cars stop and pay cash. I think this argument is invalid.
2) continues traffic, yes that is a positive thing but why would it be Turkish responsibility whether Romanian, Bulgarian or Russian ships gain one or two hours? Especially when Turkey has to pay for it? Case is that these kind of investments are always done with state guarantee and state pays for the difference if minimum amount of passages are not met.
If Romania, Bulgaria and Russia are so willing to have fast traffic, let them pay for it, let these countries bring up the investment money and carry the risks.
But we all know this will never happen, it will be Turkey carrying the risk, Turkey paying the passage difference a huge burden put on the shoulders of Turkish tax payers. I ask it again for what? To appease Bulgarian, Romanians, Russians whome ships will say "thank you Turkiye"?
I have seen no any viable plan that has calculated that the canal project is profitable (like you say "a bet on a bright future", but bets tend to get wrong (examples, bridges, highways that continuously chip away Turkish taxpayers money).
Investing in Istanbul airport is a different think, there our own national airways company (THY) is benefitting. Airways is a strategic thing that benefits Turkey even if there are costs. But a canal, what benefit is there in for Turkey? As I see only burdens: damaging environment, reserving a good amount of soil for a canal, contineously paying for a guaranteed amount of passages.
It is not like the Suez canal (ironically Turks paid for that one too) that has no alternative (like the Bosphorus free of charge)
Probably I am the dumbest person in Turkey, my IQ is not enough to see the gain.