Good point, and I should probably update the article to include something. Servo is one way, though I fear it's a bit too far out still to make much of a dent in the mobile web for quite some time. Still, it may be a good choice depending on your skills and inclinations.
There are other options too. My main ask for web devs would be to test on mobile Firefox and/or the Windows phone browser in addition to whatever webkit browsers you normally would. Actually, for now testing on Opera would probably be better than either of those; the general consensus seems to be that they're the best wrt standards.
It won't prevent the monoculture, but it will mitigate its effects and help keep the field open for competition.