The cost to charge is minimal and as pointed out the cost of battery life per mile over time and ultimately the cost to change is the bottom line.
Especially as the new 20/21700 cells come online as they are not going to be compatible with existing enclosures making proprietary battery systems unable to retro fit. Nothing the bike industry likes better than a new standard however as it keeps bike sales brisk.
This article, although over half a year old, illustrates the way the market is heading:
The future of ebike batteries according to Germany's BMZ | Ebike portal
So that "insert price point, category and manufacturer model" here bike you buy prior to their introduction will still be supported going forward and new bikes will come already equipped as soon as next model year I for one wouldn't be in a big hurry to put down the large on an e bike at this time. But because I subscribe to the open source theory it won't be a problem to retro fit any of my bikes and I predict that "hobby" type batteries with the new cells will be the first to hit the scene.
On the other hand the new cells have been in use in the Vape market for over a year and are considered to be the standard now. Make of that what you will.....