48V (or 36V, 52V. . . I can go on; but I am sure that you get the point) is going to be the same. So, there probably won't be a need for any major changes. If you are able to tinker, or know someone who is, you can upgrade the battery technology with no other big changes, other than the possibility of a new charger.

That being said, stay away from any Sealed Lead Acid, sometimes called Gell Cell, they are a dead end. However, they can, and should, be upgraded to modern batteries. So, I wouldn't worry much. The only technology change that will affect your e-bike is battery technology, and those are generally upgradable.

There will be better bikes (I forsee Mid Drive with torque sensors taking over the market), however, your e-bike won't suddenly stop working.