The fact that the source is open doesn't say anything about difficulty of implementation; in fact, being open-source probably increases the monopolising effect, since now people will be more inclined to think "that implementation is open-source, I'll just use/contribute to it instead of starting another independent one."
It might create a monopoly of browser engines, but not a monopoly of browser vendors, which is the harmful part (of course we might be heading to a browser vendor monopoly anyway, but that's due to Google abusing their market position, not the complexity of HTML).
Probably the introduction of DRM so Hollywood would start using video tags instead of flash/silverlight/other plugins. It’s a pragmatic approach, but right now it’s incredibly limited for anyone who wants to make their own browser that can load Netflix.com, for example. The only folks DRM punishes are those trying to do the right thing, everybody else can find workarounds if they need to.
