It will take a long time to make enough Semis to replace a large fraction of ICE trucks. So this will be a smooth transition where they are deployed first for duties which make it a nobrainer, like scheduled routes which are driven every day. As the market share raises, the usage scenarios will expand.
It’s hard to find exact numbers but it is likely that OTR trucking accounts for more than 50% of all miles but less than 50% of all trucks.
Many smaller companies have a small fleet of trucks for local deliveries to their branches, and some will be willing to take a look (even if just for the publicity, etc).
Only a handful of companies run thousands of trucks and could afford a small scale experiment.
Package delivery is a different beast, the vans are guaranteed to spend the night at the base every night.