Is sugar necessary for the texture of homemade sherbet? I buy pure sucralose and acesulfame potassium which I mix half-and-half and use in my iced coffee. A scant 1/8 teaspoon of the sweetener sweetens an entire pot of coffee and the flavor is perfect, almost indistinguishable from sugar. I would like to try to make (almost) sugar-free orange sherbet with that mixture instead of sugar. I have the type of ice cream maker with an insert that goes into the freezer at least 24 hours before churning the ice cream, then you add the mix to be frozen and it continually stirs the mix for about a half an hour, after which you can pack the ice cream (or sherbet in this case) to freeze somewhat harder before service. If it turns out, it will probably spend 6 hours or so in the freezer before it is consumed.

I have a guest coming for dinner just soon enough that I really don't have the time for a test run, so I'd like to know any caveats now instead of later.

My plan is to mix 1 quart of fat-free half-and-half with orange juice concentrate, dark chocolate shavings, my sweetener, and vanilla to taste. Of course there is some sugar in the form of corn syrup in the fat-free half-and-half, and there is natural sugar in the juice concentrate, but the overall sugar concentration in the mixture will be drastically reduced from what I have churned in the past.

I understand that sugar will somewhat inhibit solid freezing if I were to freeze the mixture in say ice cream trays, but what if it is churned?
That sounds to me like it'd come out completely rock hard once fully frozen. Immediately after churning while it's still just barely frozen it'll probably be okay, but I'm not sure if it'd make it through six hours in the freezer.

You have no fat to soften it (the thickeners in fat-free half-and-half doesn't really do much), and essentially no sugar (just the bit from the orange juice), so there's nothing to stop it from just freezing.

Homemade ice cream/sherbert/sorbet tends to come out harder than storebought things to begin with, thanks to the lack of softening additives and often people being a bit more conservative with fat and sugar. For example, frozen yogurt with full-fat yogurt and a decent amount of sugar can still end up solid and unscoopable once frozen, and the same can happen with more lightly sweetened sorbet unless you add alcohol. Taking the fat and sugar all the way out without compensating doesn't sound feasible.