I don't buy this argument. This is only valid if you want something exactly like WordPress that grew up like Wordpress and has all the benefits and the baggage

I don't buy this argument. This is only valid if you want something exactly like WordPress that grew up like Wordpress and has all the benefits and the baggage that comes with its unique evolutionary path. It's 2013, we have a much better understanding today of how people use the web, from how they consume to how they socialize. Many of these habits are the product of things invented between when WordPress was invented and today. With that in mind, an experienced engineer familiar with the architecture of WordPress, it's history and the web as it exists today, would be very well equipped to choose a whole host of different abstractions at lower levels, which would permit a permit said WordPress replacement to support better features more easily, where better means "fitness for use" from now into the future (5-10 years)