I haven’t been to a laundromat in ages, but we’re fixing up a house that has no washer/dryer yet and has a laundromat 200’ away. Long ago, when I lived in an appartment tower, I would go to the basement laundry room, and leave my clothes there. Worst case was they ran out of machines and somebody tossed them in a basket. And even though the odds of somebody stealing your clothes are low, most people are not as willing to leave their stuff unattended in a city street laundromat.
So how about combining the machines with a timed airport style locker system. You would insert the coins and pull out a key which you could use to open the washer or dryer. The lock would auto-reset about 10 minutes after the cycle ends, so in addition, you could put in more coins, which would act as insurance. If you didn’t get to the machine in time, these coins would be taken, and give you more time on the lock. If you did get to the machine shortly after the cycle ended, you could get back your extra coins in the coin return…
All of that could be done low-tech. Of course, more modern cash handling equipment could do this in fancier ways, and one could even do things like charge credit cards or accounts to buy more locked time. (Alas, many of those who need to use laundromats may not have credit cards.)
Obviously the manager would have a bypass key. And if your lock time ran out, with luck all that would happen is people would throw your clothes into a basket. In the laundromat was staffed, the staff could do that for you more securely if they ran out of machines, and thus make double income from the machine. (More than double — no power or water expense.)