This post is a bit late, but here nonetheless.
A species is invasive when it arrives in a new ecosystem from which it is not native. Cane frogs, zebra mussels, kudzu, and the like. You can read all about them here (http://www.invasivespeciesinfo.gov/.
Rhizomatic learning is not invasive, because it is happening within a learning space, existing on (or creating) learning networks. It is a different way to facilitate learning, and the learning happens more-or-less individualistically. Can it choke out other species of learning? Yes, within a discrete area. Rhizomatic learning has not choked out learning altogether. It has erupted as a tightly-knit space within the sphere of learning. As Aros has noted, it is becoming denser, and the boundaries more well-defined, when compared to the rest of the learning space.
Consider an ivy patch. It may choke out other species within a defined area, but it still exists like an island within the whole.
Does it substitute one form of authority for another? Absolutely. Instead of one voice heard above the rest, directing the learning, there are many voices all speaking at once. It's a noisy room, and you have to actively select to whom to listen. Even so, isn't Dave still giving us some direction? Isn't he the ring leader, the conductor of sorts? The queen (king) bee? Appropriate, as rhizomatic learning seems to generate a hive mind, or at least a hive mentality.
The great thing about this rhizomatic community of learners is that it has generated its own momentum. It started early, and if rhizo14 was any indicator, it will continue for long past the 'end' date. It will remain active as long as members contribute to it, and the traces of it will be around for as long as they are curated online.
There will be an end to rhizo15, though, some day, when the last tweet is sent, the last blog is written, and the last post written. And yet, learning will continue on; some of it rhizomatic in its own island on the vast sea of learning.
So. Many. Metaphors.