We've never incorporated anyone's code without their full participation and there's no code in Thesis I would want anywhere near core anyway. Thesis is a triumph of marketing, not technical competence. (In fact it relies on people not being able to question its incredulous claims about structure and SEO.) The few cool ideas it has were done in other themes first anyway. On a tech level, WooThemes is doing far more interesting work. (And they have been involved in core development.)