Fragmentation? I don't see how.
Yeah. So? What's wrong with having multiple plans? Your business needs change over time, it's okay.
And you could, if you wanted. But isn't it starting to get rather complicated? You have to look up pricing at that time, features at that time... It sounds cooler and making it more complex might seem like it's better, but what are you really gaining from it? How much time is it going to take to make this work? What is the risk of something going wrong?
Multiple plans fits better into your structures, covers all the requirements, and is easy to implement. I mean, surely you're not going to be changing plans every week, right? You design your plans now because you think they will last, and then you find out later that something needs to change or that you can get more conversions if you alter pricing or features, then you roll out a new plan for those people.