Sure, those are all good points. Again though it need not be done in the form of an official agreement. Just the Turks evacuating the city but holding the lines and letting the Soviets move in from the Black Sea, and then requesting an armistice. In another name a last minute desperate gamble (not unknown in WW2)
This is about as silly an idea as Sea Mammal. The Soviet Black Sea fleet is practically impotent, and the Soviets have very little shipping in the Black Sea. If several thousand Soviet troops board those few ships and steam to Istanbul, they would be sailing unescorted and vulnerable to Axis air attack from the Balkans and Turkey. Turkish air doesn't attack the troopships? That rather gives the game away.
What else is wrong with this? Almost certainly British, American, and Greek intelligence have agents on the ground in Istanbul, who will observe and report the very peculiar Turkish actions. So does Germany, and the US/UK are reading all Abwehr transmissions. (That was how they knew Double-Cross was working.) And of course other reporting agents in the Turkish government. Something this off-the-wall could never be kept to only a few, so there would be a lot of talk about it.
Turkey will go to this trouble to give the USSR control of Istanbul, to what end? To gain Stalin's "friendship"? One might as well expect gratitude from a hungry shark.
And how is this deal to be arranged? Turkey would have to propose it to the USSR, and Stalin would never take it seriously. Even if the deal was agreed to, it would take a few weeks for the Soviets to organize the expedition, and US/UK/Greek troops are already
approaching Istanbul.
The alleged constraints on Allied operations are also bizarre. Advancing north through the Rhodope Mountains to Nis and Sofia would be easier than east along the Aegean coastal plain? Troops moving along the coast could be supplied from the sea.
Greek forces have a particular incentive to liberate most of this area, which is part of their homeland.
And there is a huge incentive for the US/UK to take Thrace, which the USSR would support: it would open the Turkish Straits to Allied shipping. Lend-Lease aid could be
delivered to Soviet ports in the Black Sea., saving 6,000 km of ocean travel and 3,000 km of overland haulage.