Hard to tell. If I could predict the future, I would not be here typing this answer, I would be spending the millions I would get daily knowing exactly how the stock market would change the next day.
The problem is complex.
On the one hand, X is not up to spec with Classic, and on the other hand, Thunkable claims that they will discontinue support for Classic, and that the API 28 compiler (assuming that it eventually gets fixed, since it is buggy) is likely the last iteration.
However, with Classic, you can actually download your aia and upload it in App Inventor, AppyBuilder or Kodular and continue development/deployment from there with just a few corrections and adjustments. With X, you cannot get anything out of the system for safekeeping or to migrate – and that is assuming that there would be something compatible out there to migrate to, which there isn’t.
On the other hand, App Inventor is supposed to work on adapting their development environment so that it could also target iOS. It is not happening fast, the note claimed they the envisioned it for “summer 2019” which officially ends this coming Monday September 23rd (so don’t hold your breath).
Those in the know claim that the problem is due to the lack of cooperation from Apple, which likes to control everything (they insist on you developing using their environment, using their computer language, on an Apple computer, distributed only through their App Store, on their conditions, with you paying a yearly fee. With Android, you can even side-load; that is, install an app from a site that is NOT play.google, if you know and accept the risk.)
But if one day, Apple can be reasoned with, and that App Inventor is allowed to produce files that could target an iPhone, then all App Inventors derivatives (Kodular, AppyInventor, and even Thunkable Classic, if Thunkable decides to not play the heavy and kill Classic) would most likely ALSO become Apple compatible.
If Apple is that unenthusiastic now with the App Inventor porting, what is to say that, 6 months from now, they would decide that X is not to their liking anymore and basically kill it off for iOS? Apple even implemented planned obsolescence in their own products (and is being sued for that) in order to force users to upgrade to their latest models, so it has been seen before that they can decide to be somewhat nasty and uncaring.
If you insist on having iOS support, I would suggest you also investigate the other possible approaches, that of apps running as browser clients. There is one web for everyone, and no such thing as web pages that would only load for Windows, or only for Apple, or only for Android, right?
That means if your app is running using the components of a browser – any browser, since they ALSO have to be standardized, be it FireFox, Chrome, Opera and what not – then you immediately become portable.
The downside is that tools for developing that kind of applications do not have the nifty “click this number 5 tile to the end of this assign to variable tile” approach, and you would have to type code in the old fashion way.
That is my two penny’s worth.
For the record, those alternate development environment able to support Apple and Android are Apache Cordova (formerly known as PhoneGap), Enyo, Microsoft’s Xamarin, Facebook’s React Native, and Google’s Flutter.
There may be others that I haven’t heard of.
And I am just about to proceed with evaluating them, so would be hard pressed to recommend one over the other, although would most likely start looking into Flutter, primarily because it is the one most likely to be mercilessly optimized.
But that is just me.
(as for your question being long and needing someone to ‘bear’ with you, how is THIS for an answer???)