So far I've been having a blast with UIFlow on the Paper.
I have encountered an error, though, when using "Http Request"

When the code is Run through the IDE it works fine but when the code is "downloaded" to the device and an HTTP request is executed it errors with exception OSError 118 which I guess means the wifi is having issues in the application mode but not Run mode.

I was able to code around this by adding an additional "wifiCfg.doConnect('AP', 'AP_Password')" before the code is executed.

Other than that it's fantastic using UIFlow for development!

I have written a simplistic application with uiflow which exposes the micropython interpreter: https://github.com/follower46/m5stack_fake_repl

So I did find the REPL: https://github.com/m5stack/M5-3D_and_PCB/blob/master/FACES/m5stack-micropython-tft-repl.bin
I haven't tried loading it yet

I've been trying to find a REPL which works with the keyboard face.
I started writing a simplified one (using exec/eval commands) but I was curious if an actual one already existed.