Regardless of future mainstream appeal, I don't think Julia will meet the same fate as Lua in the area simply because of how simple it is to create and maintain

Regardless of future mainstream appeal, I don't think Julia will meet the same fate as Lua in the area simply because of how simple it is to create and maintain DL libraries compared to Python. Multiple dispatch, native matrix support and high performance out of the box (plus native and composable GPU operation libraries like CUDA.jl) means anyone can write their own DL library from scratch in a few thousand lines (and there are tons of those already, even if the community converged mostly into Flux, with Knet as a second option).