It has been asked many times if Lubuntu was going to support this. This certainly was a relevant question for 18.04, but since we've switched to calamares and 18.04's official support has ended, perhaps not.
On the other hand, there is an advantage to being able to install the system without a network connection which the mini.iso cannot do. Also, the way it is exposed in ubiquity, it's very easy for the user. There's no having to figure everything out.
There is one other caveat, though: this feature as we know it is a temporary solution. The new "Next Generation" installer subiquity is supposed to replace ubiquity and will supposedly be more flexible, allowing for such things as a minimal install. Whether or not the way we see it today is the way it's going to be is anyone's guess.
That said, it would nice if we could figure something out, or at least decide whether or not we're going to bother.