Bikes are durable goods that should last decades. If you don't plan on trading in every few years, buy an electric that has replacement motor, control unit, battery, etc, easy to obtain and at reasonable cost. For ANY motor. My hope is that over time, the industry will adopt standards for frame interface (mid-drive), and have multiple brand motors available as replacements.

When Bike Friday designed a new electric bike because their previous motor and battery suppliers went belly-up, they chose Bosch, as they felt they were the least likely to have supply issues in the future, and have a good quality reputation. Unfortunately, the Bosch motor cannot be retrofit into older electric Bike Fridays, it's completely different mounting, the Bosch is mid-drive. The older bikes were hub-motors, so a new wheel could be built up. The old batteries separated into 3 layers to be legal to fly with, the Bosch battery cannot do this, but BF just debuted new batteries that have that feature.