Removable tanks like BBQ grills and smaller RV trailers, etc are not difficult to get refilled or replaced in most markets. If an exchange service is all that is available many customers won't want to exchange a new or nearly new tank for one with a unknown history. That's completely understandable.
Larger trailers with 30# cylinders are a somewhat different story since there are few to none in the exchange systems simply due to demand vs expense. A new 30# steel cylinder is at least double the cost of a new 20# steel cylinder.
The OP mentioned having trouble finding actual refillers for his company's sweeper cylinders. The 20# and 33# cylinders used in that application are not typically involved in exchange service unless it is done by a company who delivers to your business. Those would generally be propane companies and welding supply companies. Nearly every welding supply company has propane available in cylinders, either as a walk-in or delivered item, some refilled on-site some exchanged. That may be a solution to his problem for his sweeper cylinder refills. Unfortunately for smaller users welding supply companies are frequently way over priced for small LP purchases. Many times the price may be negotiated based on long term commitments and annual volumes. Very few of them are set up for RV tank filling like our frame mounted tanks on our motorhomes.
Regardless of all the above thoughts and opinions, I don't see propane being impacted in any significant way by the trend toward more all electric motorhomes, it is simply not that big a part of the market. I'm not even convinced that the trend is customer driven. It may be an effort by the manufacturers to eliminate an additional system which must be included in their designs and can be eliminated and replaced with the all electric at far less cost to them.