I'm a bit of a vampire, I spend the majority of my productive hours in the dark or in low light environments. I play around with Android and my Samsung Galaxy S7, as well as many devices today, make use of an AMOLED display. I think a dark theme would be a great addition to this app.
The benefits of a [True Black] theme for these devices can be found here:
I encourage you to read that, it is a bit of an eye-opener.
I'd like to draw specific attention to "...to really save juice you need a true black (as defined by the #000000 hex value)." Anything else and the pixels remain on, it must be [#000000].
This is just one explanation of why this might be a good idea and where that link above came from:
Not only do I genuinely just like dark themes better, it is far....far more efficient on AMOLED devices, and it is easier on the eyes in low light areas.
As far as the difficulty for the actual implementation of features goes, this should be chalked up as being pretty darn easy to implement. I feel as though this type of theme should be standard and it is a shame it is not optional within this application's settings.