There’s a lot to unpack in Yahoo’s reported $1.1 billion deal for Tumblr, but much of the reporting today is focused on the rather bland challenge of turning Tumblr into a profitable company. Forcing Tumblr to make money will eventually become an important mission for Yahoo, but for now it’s far from the point.

This deal’s most pressing issue isn’t what will come of balance sheets, it’s what will come of each organization’s corporate culture. Marissa Mayer has promised, in her post on the deal, “not to screw it up.” She’s talking about Tumblr. But that’s just Mayer’s very smart way of inverting what she must be hoping Tumblr becomes for Yahoo: a threat to its older, established, some might say calcified culture that has been short on innovation, creativity and user-focused design for many years now. Tumblr, indeed, will be far from “screwed up” as it gets used to its new home under Yahoo. Tumblr seems to have a bright future as something like a design lab and an already-functioning charter city under the aegis of the Yahoo brand. It will be, and already is, something Mayer will point at to tell her team, “why don’t you do it that way?”

When Mayer was at Google and led all product management and design efforts, she famously relied on data about user behavior to inform her “design” choices for Google’s products. At the time, some argued that her method of, for example, choosing one shade of blue over another because it made users fractionally more likely to click wasn’t really design at all.

Tumblr has, in some important ways, already been living by this design by data principle long espoused by Mayer. Most importantly, Tumblr is not trying to offer products to its community by throwing nonsensical new portals and features and widgets at them, the way Yahoo has for years. Rather, it’s given its community a platform, staying out of the way when it comes to all but the most fundamental underpinnings of the site. Sure, it’s got lots of handy defaults for new users, but ultimately Tumblr is whatever its users want it to be, and it’s different for every user. That’s precisely why so many different types of communities, from design bloggers to GIF makers to bored high schoolers, live on Tumblr, and why Tumblr doesn’t have to overtly try to attract new users–its platform is already doing the job.

The Tumblr-Yahoo deal isn’t about two tech companies linking up to share strengths. It’s about two entirely different ways of doing business being pitted against each other to do battle in the meeting and boardrooms now controlled by Mayer and her trusted deputies. It’s pretty clear what camp Mayer will likely favor, given that she came from the company that helped kill an earlier iteration of Yahoo. The problem is that Yahoo’s portal/agency/sales-culture DNA is still in many pockets and products across the company, however dormant. So, possibly, is Yahoo’s propensity for killing or starving to death its acquisitions, as it did with an earlier generation of once-promising startups. (Hello Delicious! Hello Flickr!) By making such a strong oath to Tumblr, Mayer is basically throwing down a challenge to her team to move forward or get left behind.