Webkit was the only thing the mobile web had that apps did not: a mostly un-fragmented codebase. Now developers will have to test their mobile web-apps against even more browsers reducing time-to-market efficiency. Hopefully competition will lead to faster improvements by top players (Google), but the more likely scenario is the least incentivized player (Apple) will drag their feet re-creating an IE6 scenario where one browser will slow mass adaption of standards.