So,, with that being said , will they have to stop making them for the value to rise noticeably , or are they rare enough to at least not to depreciate much , I wonder
OK LONG POST.
In Europe, the Fiesta is the most popular car sold, with the 1.0 leading the pack. The ST served as a halo car (now the ST200) and it did its job well. WRC, Rallyes, endorsements, test drive days, Top Gear. As a result, values of ST models will most likely rise as the FiST is literally born of the same Euro blood as the XR2, Cosworth, and RS badges of Europe's past.
Now in the US we like horsepower and tire smoke. Understandable; we grew as a nation with highways. American culture is Grease, Fast n' Furious, Santa Claus. Also gas is cheap even when its 4 bucks a gallon. This favors the GT350s, and Hellcats of the world, as well as our trucks. Small, sporty, cheaper cars historically don't do that well in America, unless it receives unanimous praise and/or a dedicated cult following. Example: Beetle, classic GTI, classic CRX/Civic Si, Miata.
The worst I could see actually happening to the FiST would be similar to it's "father" the Focus SVT. A short production, a following, an aftermarket, but not making any impact on mainstream culture which results in prices not really going anywhere but down with possibly an uptick after 25 years. Don't expect 30 years from now that the FiST will demand figures high enough at an auction house to cover total cost of ownership which really adds up overtime.
Now time for more predictions.
A) No NA Next-Gen. Dedicated fan base, low production, motorsports/halo/drivers car status, reliability = slowed depreciation,
B) No NA Next-Gen. Fan base falls apart, low production, no clean/stock examples = forgotten, examples in good shape sell higher
C) A mix of A and B.
D) No NA Next-Gen, but somehow a FiST becomes a hero car, movie does insanely well = movie legend status
E) Next-Gen FiST sucks = dedicated following for 1st Gen continues, FiST is soon no longer offered in NA due to poor sales, back to A and B
F) Next-Gen FiST improved = everyone trades in for new model, 1st Gen falls victim to high school parking lot status, and a whole number of things can happen here afterwards
G-Z) ....etc....etc...etc
It helps to be a future classic, but this was thrown around alot when the FoST came out, and the FiST, and the RS (which could be more of an "true" with a limited number produced). But the "true, red, white, and blue" classics from Ford will always be the GT, and all your "special limited race snake edition Mustangs", possibly the V8 Raptor.
So to answer your question, "Will they have to stop making them for the value to rise noticeably?" Yes and No.
Your second question, "Are they rare enough to at least not to depreciate much?" You guessed it, Yes and No.
The only thing that is fact is that we have an uncommon car that will become more even more uncommon/rare.