GEM v. TTM

"The first approach is, in many ways, more pleasing. But it implies that the GEM API could
change significantly over time. And that, in turn, could delay the merging of the whole thing;
the GEM API is exported to user space, and, as a result, must remain compatible as things
change. So there may be resistance to a quick merge of an API which looks like it may yet have
to evolve for some time. "

Why? If it's not standardized anywhere, you coul just label it experimental and actually try
it, before starting to say that it will remain compatible as things change.