Cool!

Don't get your hopes up too soon for radon-detecting plants.
The mechanism discussed is one that operates at a chemical level that requires a certain concentration of target substance in order to produce a detectable signal, even when amplified as discussed. On the other hand, radon and its progeny, even in a "problem house," would be present at extremely small concentrations when considered from a chemical perspective--many orders of magnitude smaller than the bacterial metabolites that have been detected. And while the kind of chemical damage caused by radon/progeny in cells may be something that could be looked at, many potential chemical markers for that aren't specific to radon. The author writes, "If they can figure out how houseplants respond to other threats, such as radon..." but I'm afraid this may be spitballing, at least where radon is concerned, leading me to think that that is a very big "If".
I doubt that radon testing professionals are likely to be replaced by genetically engineered tobacco plants anytime soon.