The thing is, that support is very flexible. Nouveau is sending it through TGSI to take advantage of their current driver support. AMD is sending it through an entirely different LLVM pipeline. There's no reason Intel couldn't just copy and paste their Beignet code into the same framework, getting the benefit of some shared code in the front while keeping their same custom backend code.
Except, they are apparently allergic to anything named Gallium that might actually work to benefit their competitors. So, we get a completely separate out-of-Mesa support that shares no code at all. Similar to Mir, the original announcement came with a bunch of technical reasons behind the decision, which were all quickly outed for bullshit within a couple hours. Since then, there's been no more discussion at all about why beignet even exists, other than, well, they'd already started it.
Yes, I agree Intel has every right to do whatever they want to do with their own time and money. Just as I'm free to call them out about what i think is stupid.