Opera's decision to stop developing its own HTML layout engine and use Google and Apple's WebKit may end up being a good one for the company, it's too early to tell, but it could happen. But it's very unlikely that it is going to be good for the web at large.
Reactions on the web range from circumspect to worried. Even Opera people don't seem particularly enthused or confident in the new direction.
Mozilla's Robert O'Callahan, who works on the Gecko engine, is rightfully worried about the move.
"It's a sad day for the Web, since I thought highly of their Presto engine and their Web standards work. Their impact on Web standards will be dramatically reduced, especially where they want to do something differently to Apple and Google," he writes.
WebKit already had too much power, especially on the mobile front where it's essentially a monopoly. Opera adopting it doesn't help.
The reason why Opera was forced to make the switch is precisely what will get even uglier, support for web standards. More and more developers don't write websites or web apps based on standards but based on what works in WebKit.
That's almost universally true on mobile. With one of the four major HTML engines gone, developers have even less incentives to support anything other than WebKit. There was already talk of a WebKit monoculture.
The problem is that, with so many people using WebKit and developers only targeting WebKit, web standards become moot. WebKit actually does a good job of respecting standards and is open source, but it's not perfect, no engine is. This is why engine diversity is important, to keep everyone else in check.
"Web standards would lose all significance and standards processes would be superceded by Webkit project decisions and politics. Webkit bugs would become the standard: there would be no way for developers to test on multiple engines to determine whether an unexpected behavior is a bug or intended," O'Callahan warns.
In the end, this puts even more pressure on Mozilla. In the desktop space, Gecko is one of the three rendering engines that matter. In the mobile space, it's essentially one of two. This while Firefox's market share on mobile devices is minuscule at best.