At the Magento Developers Paradise in 2010, then CTO Yoav Kutner announced Magento 2.0. Later that year, Magento announced that we could expect a stable release somewhere in Q4 2011. Today, 3 years after that first announcement, we haven't even seen any sign of a beta release. At the time, the developers already realised that Magento needed a major code overhaul to support the growth of its customers and to keep up with the fast growing e-commerce world. So instead of building upon the 1.0 codebase, they decided to start from scratch to have maximum flexibility and to make development much faster. Oh, the irony. In the fast-paced e-commerce world that's, that's (very) embarrassing. If eBay doesn't get its act together, Magento customers will fall behind the competition and switch platforms. The original announcement can be viewed on YouTube.
Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.