Depends on how you perform the upgrade. I'd recommend backing up what you have and just trygit stash git pull git stash apply
It should probably just work, but you may get "merge conflicts" that you'll have to resolve.
Just been reading this, looks good, from what I can fathom.
I don't want to express (ha, get it) too strong of an opinion here, but I personally feel that the way the old express core team handled the Strongloop buyout was unnecessarily negative. It seems Strongloop is doing very much to make express even better, so I am all for it.
It reminds me of when Stripe assumed control (with the author's permission, of course) of the stripe-node library. Within a week, every single issue had been closed, and the documentation consolidated into stripe.com.