A few questions: That's unexpected, especially if you have a good multicore CPU and use all cores for building. The only downside in crosscompilation in Mer SDK is ARM emulation through Qemu, but other than that - multiple cores speed things up a lot. I guess when more powerful multicore ARM computers will come out - that would be compensated. When compiling fennec on dual core x86_64 machine - it can take quite a time (that can be tweaked though to avoid running python through Qemu in scratchbox2).
Why would chroot on ARM be easier to install than chroot on x86? chroot is chroot whenever it is, no? What can become simpler is avoiding using Qemu and stuff, since it's the same arch.
How would size differ? I understood the only difference would be in putting the chroot on the ARM host, instead of the x86 one. Size wise it's the same bits (except may be minus need for Qemu as above).
Other than that - it's surely useful to have an option of ARM host for this.