Hi @prince and @cduvallet,
I think I know whats going on, although I'm surprised conda didn't error.
First just to get our ducks in a row, run:
qiime dev refresh-cache
(This shouldn't matter, because it automatically detects new versions and re-runs itself as needed, but if everything was working as expected we'd see perc-norm in the list...)
What I think may have happened is the conda build for q2-perc-norm uses Python 3.5. As of 2019.1 we switched to Python 3.6, this means existing conda packages should be rebuilt for 3.6 (or built as no-arch).
We haven't made any changes to the plugin API, so q2-perc-norm should still work with the latest QIIME 2 version just fine. What we could do is perform a source installation instead which won't have the issue with Python 3.5 vs 3.6
If the source installation doesn't work, then something much stranger is happening.