Do you have benchmarks for running a tex engine on a tablet CPU? Everytime this topic comes upo on comp.tex the consensus seems to be that tablets are not yet capable of running tex on the fly.
What slows TeX down is that many packages use extremely elaborate abstractions, which all need to be evaluated using string expansion. These days you shouldn't be surprised if some package is using floating point emulation with TeX macros (https://github.com/latex3/svn-mirror/blob/master/l3kernel/l3...) behind your back. Handy yes, but certainly not fast.
Probably not for a whole book, but for a single chapter? Almost certainly. And if you eschew the features of XeTeX or LuaTeX and just stick with pdfTeX, things could be very quick: For the example I posted elsewhere in this thread of typesetting a novel in 30s with XeLaTeX, pdfTeX does it in about 6s. A single chapter (32k of text): 0.8s, and I/O bound at that. Even if a tablet's 800Mhz Cortex A8 does that 5 times slower than my Core 2, it's fast enough to be done speculatively. It's certainly no slower than loading a web page over the internet.
(For comparison, when run on the slowest CPU I have handy, a 1.5Ghz Athlon XP, the single chapter takes 1.5s wall time and 1.1s CPU time.)