Running the Austone is a good idea Kai. Here's why...your set-up, and sidecars, have one thing in common. They both have to be steered
instead of leaned.
Steering causes the rear tire to be scrubbed, meaning dragged sideways as opposed to just leaning like on a 2 wheeler. Motorcycle tires are not designed to withstand a lot of scrubbing action, so a car tire is a logical choice here. On a two-wheeler, the car tire handles poorly due to it's configuration, though some people don't mind this. In your case, handling is not an issue so the car tire is perfect. I mentioned this a few weeks ago in a different thread, back before you revealed you had got a Voyager kit, but you didn't seem to want to believe me about the motorcycle tires failing in 5K miles. I guess you must have investigated this more and found out. I made some other derogatory comments about the Voyager kit as well, but, to clarify, that was about the kits manufactured early on in their conception. Perhaps some of the issues the early kits had were ironed out through the years, I don't know, I only have the one experience with one I helped install in the early 1990's. I wish you the best of luck with it. Truth is, I don't like the true trike kits either. I helped install a Champion trike kit, also on a Goldwing (the same one we removed the Voyager kit from), and when I rode it for a test ride, going around a corner I got it up on 2 wheels which scared the living shit out of me. I guess if you did it frequently maybe it wouldn't be so bad. I can get a sidecar rig up on 2 wheels, and it's fun and very controllable to me, but then, I have a lot of experience doing that.
Any way, like I said earlier, I really do wish you the best of luck with it. The front tire wear won't change much, you might lose a little up front but it's negligible. You may have to reconfigure your Voyager pre-load for the taller car tire if / when you make the change, but other than that you should be good to go.