When I went GT350 shopping late last summer, I saw very few optioned with the "convenience package." At 6'2', 214 lbs, fairly hwp. I did not have a problem to get into the Recaros, sitting in them was marginally ok, but getting out of them with the very high side bolsters, was literally a pain. Not a big surprise for a guy in his sixties who played 12 years of football and some hard military under his belt. Plus, I was not impressed with their range of adjustability - or lack of it. As an alternative, the leather seats were far more comfortable, had heating and cooling and still had more bolstering that the seats that were in some of my C5 and C6 Corvettes.
And let's get real for a moment. The GT350 is a fine and pretty unique sports car, but it is NOT a race car. Race cars do not have individually controlled climate control, satellite radio, navigation, lots of internet apps for your phone. Sure, with minimal prep, they are fine for autox and the occasional track day. And for those of us who might want to take a trip in their car, and maybe even take their spouse, these seats make a lot of sense.
If you want to get a step closer to a race car, buy the "R" and make sure not to add back in the radio, Nav, rear seats.... Use the extremely marginal street Pilot Sport Cups that last for maybe 3000 miles and are downright scary in any heavy rain. I had them on one of my Vettes, so I am familiar with their "painted on" tread look. I doubt more than 2 percent of the people on these forums could use the "R" to 100 percent of its capability. And if you had a portion of Jay Leno's income and pull with Ford, then you could get your "R" delivered with the convenience seats like he did.
So lets talk availability. It took me over two months late last summer (using Auto Trader) to find a convenience package car in a color combination I wanted. In '17, Ford underestimated the popularity of this package and simply did not plan for producing enough of them. Perhaps they thought that all their customers for a $60k + car would be twenty somethings (mostly who cannot afford the car)or maybe others through their 50's who other demands on their incomes such as families/children/college tuition.
I do not have any idea what percentage of the '18s will offer these seats. But its your money, don't let someone "seat shame" you into something you really don't want. You would be surprised how many people who saw my car told me that they wish they had these seats.
Good luck in your search!