As you said, you are "no expert on the subject". Irrespective of what you think, or what is realistic, or what makes real economic sense, the Turkish government moved in early September of last year to BAN the use of foreign currencies in a host of uses domestically. There are loopholes for dealing with international trade and crucially, which is obviously where they are getting it from here, the use in international business.
As for what the yearly product is aimed towards, if not aimed at Turks, who is it aimed towards? Any big frequent flier would not bother with this product whether they are Turkish or foreign, as their status with most airlines would already cover most of these services that matter (namely all the fast track stuff). This product targets what I call "medium travelers", those that travel frequently enough that they might need the services, or those that fly lots of different airlines, and none enough to have status, and crucially those who are not already flying in Premium cabins, and are doing it for a long enough time, that they would think of getting the service after a long enough time. Furthermore perks such as parking are aimed towards Turks, as most expats living in IST would not normally leave their cars parked at the airport, as a matter of fact those having "Blue Plate" cars, (many expat workers for multinationals and consular personnel) would never do so.
Crucially, unlike TAVPassport, this service is ONLY for ISL, not a group of regional airports such as the TAVPASS (TAVpass also worked at a bunch of airports inside and outside of Turkey such as Ankara, Izmir, Bodrum, SAW, and even Tbilisi I believe) so it was a value prospect for Turkish frequent fliers, especially those who flew Turkish LCC's.
As for "menu costs", for the normal Turkish public, that is the way things have been for decades, and that is just the way it is. Lastly, the Turkish "worker" diaspora is NOT at all the market for this product, never has been, and never will be. The market for this product is notionally either the Turkish sales manager whose company sends him frequently all over the place on the cheapest possible ticket, whatever the carrier, and he feels that he can "treat" himself, or get the company to pay for it for that reason. At these costs, he/they ain't going to bite.