A lot of things can change between now and next year.
By your own admission you won't be ready to show before then, and everything else about this barn and instructor seems to suit for now, right?
The barn or the trainer might aquire some suitable horses between now and when you decide you want to start to show.
You may decide to forgo training until you're at a higher level of competence so you can get more out of the experience.
I think you're worrying well ahead of time
There will also come a point in your lessons when you can discuss with your instructor that you would like to show, and ask him how that could be made to happen in the current venue. He may know of something suitable for you to show that you haven't considered.
Also, most successful instructors and barns have certain niches and market to that niche. If this instructor's and barn's niche is giving beginners a correct foundation, then they probably understand there's a certain point at which students need to change barns if they want to continue to advance.
Yes, sometimes there is jealousy and hurt feelings when students or clients change barns, but just as often there is an honest conversaton, following by the instructor giving a recommendation and making a referral phone call for the student.