I don't know if this will be of any help to you by now, but I decided to look out my old Airport Express to access a USB printer that's 'supposed' to be wireless but doesn't seem to like my router (printer instructions poor so I might be missing something but its wireless connection needs setting up from scratch each time, which is just too much bother!). Having reset the AE but still not been able to see it with Airport Utility, I decided to look on these forums and found this thread, where I see that model is not supported on recent releases of OSX.
I thought maybe I would be able to connect it to the router (and thus to my computer) by plugging it into a powerline adaptor next to the printer, which is in another room, currently plugged into my husband's Mac, which needs to be on for me to use the printer! I need to get a further powerline adapter in there anyway, for other purposes.
Anyway, I have found that plugged into a powerline adaptor my old Airport Express appears to be working fine as a bridge without any IP address (plugged my iPhone into its USB port and it found my Mac OK), so that will work fine for my purposes.
Now, as I'm writing this, I find that my iPhone with iOS9, can see the Airport Express wirelessly, even though my up-to-date Mac can't, but gives me the message that it can't be set up by the software. I'll see if I can get one of my old Macs up and running to switch off the wireless signal but otherwise it will be fine to use once I've got a new adaptor and I'll only be switching it on when I switch the printer on.