I asked the lead dev about custom maps and he might consider it, also they thought of going open source or selling it.
Its a tough call.
I tried modding Volo 0.02 and i managed to do some stuff ( removed trees, you can remove clouds, sound without crashing )
I used some Unity Assets Explorer
Try your luck. Also there is still link for volo 0.02 and even 0.01 but early Oculus rift build link dissapeared but rumor has it older builds lay berried in a far away bay where pirates hide their stolen treasure. Some builds also on steam.