added a comment - - edited
OK, so I have some additional interesting facts. It does compile and work (where "work" is defined as "renders a thing from the npm module").
cljsbuild: 1.1.7 via lein
Heap size: 2g
npm-deps: react, react-dom, and @blueprintjs/core
cljs deps: Om Next
Project is an om-next app, so cljsjs.react is in the classpath
Building the application without the npm deps and no code that refers to them: 46 seconds (CPU time)
Adding the NPM deps (with install true, but no code that uses them) increases this just be the amount of the install: 59 seconds
using the npm deps increases compile time to: 3 minutes 50 seconds
Critically: with verbose on, I can see that om/next.cljs takes about 15s in the first two cases, and 3 minutes in the final one. In other words: the thing that is slow is compiling next.cljc. Nothing else gets slower.
I'm not sure if this is even going to work "right" when it does compile, since I'm not sure how the cljsjs.react and npm react can co-exist (this is where I assume Om Next probably just needs to be made to use npm instead of cljsjs?)
But, since I saw that Petter was pulling in similar deps, he might be hitting a similar problem with cljsjs.react and npm react both being "in scope" so to speak.
When I use it from figwheel, the time between reloads becomes unusable. I assume it is related, but I have no data to back that up.
EDIT: I had missed the new doc on :global-exports. I'm going to try that and add my results.