When my little sister was very young, we told her that the ice cream truck was a "music truck" - it just went around playing music for people.
I don't necessarily recommend lying, but it may have prevented some tantrums...
The app concept would be difficult for a startup since you need to both introduce the truck and the app at the same time - it's a two-sided market. An existing coffee company would have an easier time, since their customers already have the app; they just need to add the feature to the app and start sending out the trucks.
For what it's worth:
I have seen plenty of mobile lunch trucks. These often drive around industrial streets, visiting the parking lots of companies too small to justify their own cafeteria and too spread out in the suburbs to walk anywhere for a bite to eat. These trucks would have wrapped sandwiches, some Popeye's chicken combos they resell, coffee and cigarettes. They would usually honk several times on approach and would sit in the parking lot for 20 minutes before moving on. I wouldn't say they made anyone rich doing it but it was consistent. So that leads to the question, what neighbourhoods would this truck visit? Office parks? College campuses?
That brings me to the consistency part of it - If there was a mobile coffee truck, it would have to be consistently available. Since coffee is not the same as lunch with regards to an obvious time to sell it (okay aside from your morning commute but then you're also driving?), your customers need to know that it's available when they want it or they just won't bother. There's also profit margins - How much do you have to price a truck coffee to make it worth it? And how much do you need to sell?
That also makes me think of demographics - I've worked with two types of people, those who want their coffee as cheap as possible but lots of it, and those who wanted the good stuff (Literally quantity vs quality). Can you satisfy both or do you pick one?
A coffee truck could work if the goal was to get neighbors out of their house and get them to chat. The coffee truck rolls up, the stay at home parents and people working from home all come out at the same time. They order their coffees and stay in the street chatting after the truck leaves. If the truck had an espresso machine or other beverages (macha, ginger beer, etc), it could provide drinks customers don't have at home.
If it were legal, a cocktail truck, or even a weed truck, might be an even better business idea because it taps into the same relaxed impulse-buying that ice cream trucks do.
A possible challenge is staffing. You'd need an employee who can switch between driving a truck through complicated neighborhood streets (pedestrians, speed bumps, lack of a grid, figuring out where to pull over) and preparing potentially complex drinks all day long. Your employee probably needs to either prefer that setting over working at a coffee shop, or you need to drive more business with the truck than a typical coffee shop does so you can compensate them better.
An app requires onboarding. I think it might be better to just play music that sounds different from an ice cream truck. Pick a limited route and drive it routinely. Have a big sign on the truck that explains the business model. You run the risk of annoying people daily with music, but you need the music to cue them to come outside.
Another possibility would be some kind of "summoning" app. Let people freely indicate via the app that they want the truck to drive into their neighborhood. The truck can then take that into account when deciding on its route. If there's only one request, the truck can still go there. The driver can potentially indicate via the app where they're heading to next and what requests they're responding to. Then it's "better than doordash" because requesting the delivery is free and has no commitment. And if the driver responds to requests, then users get a feeling that their input actually matters and become more likely to use the app.
Being able to take orders via an app might be nice. So it would be a bit like a hybrid doordash. If somebody puts in an order, you drive there and deliver like doordash, and charge a premium for the delivery. But you're also driving around all day. You can discount orders that are pickup, meaning that they'll come to your truck to get it wherever your truck happens to be.
Potentially you could carry pastries, like a coffee shop. Maybe bread too, eggs, sandwiches, other breakfast or lunch items. Many coffee shops source their baked goods from local bakeries, so you wouldn't have to bake them yourself.
A nice aspect of this setup is that you wouldn't have to pay rent to park a food truck or rent out a brick and mortar. However, you'd have to pay gas and maintenance costs, so it may or may not be a true advantage. Refrigerators on food trucks are notorious for breaking because they're designed for buildings with more insulation. If you could avoid the need for refrigeration, you might have an advantage over the issues that come with food trucks.
It's a relatively cheap experiment. You can buy the equipment used. If it doesn't take off, it should still have most of the resale value. Seems like it should probably be launched by someone who already knows their way around an espresso machine and intends to be the owner/operator and has a passion for the work.
I sometimes wonder if the world should have coffee trucks, like ice cream trucks, roaming the street. Especially when half the population is working from home.
Coffee seems ideal for this because:
There are clearly stationary coffee trucks, like food trucks. I think moving trucks may also exist or have existed ever, but I don’t think I’ve ever seen one, and it’s hard to find mention of them. Here are some people who had the same idea, but since nobody was expecting a moving coffee bus, they got more traffic sitting still like a cafe. But surely people expecting your product to exist is an obstacle not unique to circulating coffee trucks. Here is someone with the same idea, and someone who says there was one in a holiday park once, and some others who think they exist in Australia and Buffalo, but it sounds like they might be thinking of stationary coffee trucks.
I’m not sure that it’s good for any kind of truck to exist if it makes noise all the time as it travels through neighborhoods, delighting some, but surely disrupting others. But I think that can be entirely resolved digitally: instead of the truck playing music, the service could have an app that plays music when truck is approaching, if you signed up for that. Then you touch the notification to turn off the music and at the same time report whether you want a coffee.
Am I missing something?