Small battery powered OpenWrt based device, sure. Travel routers are a prime example.
Using a display for anything other than text alone will be a significant challenge since there are no graphics drivers in OpenWrt (aside from text output). Beyond that, it depends on what you are trying to do... OpenWrt is first and foremost a routing/networking OS, so that's what it does best.
What are you trying to do with this display and device?
I'm building a prototype for medical device that needs to have e-ink display and power small external grid of smart leds via i2c or similar protocol. Idea is that to conserve power device should go to low power mode in order to be operational for days/week via battery not just hours as other OpenWrt devices.
It really depends on what low power means to you, what kind of tasks the device should take care of, how long the battery needs to last on a charge and what capacity (size, at some point also safety- and maintenance considerations) you can install...
From the outside, this sounds like more of a job for something like esp8266/ esp32 (and even that isn't really suited for weeks without charging).
[quote="valentt, post:3, topic:167167"]
Idea is that to conserve power device should go to low power mode in order to be operational for days/week via battery
As @slh said, it depends on the battery (from a hardware perspective) and many other things... but OpenWrt as an OS doesn't really have a feature to run in an ultra-low power mode (i.e. a sleep/hibernate type mode) since it is really designed as a router OS.