According to Mathias & Paolo the combo of C & JS that they use is actually much friendlier in terms of resource requirements if they can get beyond some of the ways in which they have to work around modern OS limitations. They are talking about building a pear phone too.

While there are a lot of caching improvements that need to be made Keet is actually really impressive even in its current form & it works fine on mobile. Holesail (Liveport) which also uses Pear appears to be very lightweight & reliable. 

 Bare (By Holepunch) is a lightweight runtime, Keet gives pretty good performance and stays up to date with latest content even when it is all P2P. 

Similarly Holesail runs on pretty much everything even though it is Nodejs based.

I don't think we need to worry so much about "Low end devices" here. 

 amen