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.