As with all things horses, the answer to if it is a viable source of income is “it depends on lots of factors.”
In the areas I’ve lived in, I’ve not seen anyone with a personal farm/indoor allow ship-ins. I’ve only seen boarding and/or training facilities offer the option, and the haul-in fee varies wildly, I’ve seen anywhere from $25-100 per use. If you’ll have one of few indoor arenas in the area, you can charge more. If there’s lots of options, you’ll likely have to charge a lower amount to stay competitive.
Some facilities offer a flat monthly rate, and you can haul-in as much as you want. Boarding facilities already have, or expect, a fair amount of traffic on and off the property, so if you’re not used to that, the added work to clean up after a bunch of strangers all the time might not be worth it.
Some considerations:
Arena size - will it be big enough for multiple people, or so small that only 1-2 persons can ride at a time, and no one would be happy jumping in it or doing much more than walk/trot?
People will need to use more than just the arena - do you have enough space for trailers? Grooming?
Will you allow haul-ins of any discipline, and how will you coordinate what’s going on in the arena? For example, I’ve met lots of reiners that don’t like to ride with jumpers, and vice versa.