“Up & Coming Extensions”.
In plain English, this means extensions that are under development but have not been published, yet. Is that what you really mean? That is, you just cannot get it now.
For example a phrase like “the up and coming Ford Mustang III” means a new model of car that is under development but it not in mass production, yet, and it certainly is not for sale or rental, yet.
The “up and coming President of the United States” means that he has been elected, but he has not entered office, yet, or been sworn in. Hence, he is not really the President, yet.
We really wish that you would be precise in the statements that you make, and that you avoid any kind of ambiguity and slang language.