How will Omega 4 play with Layout if at all?

That module was a proof of concept. No more, no less. I am against layout builder UIs because the outcome of whatever you click&point configure there is never going to be as good as hand-crafted HTML & CSS layouts. Furthermore, the current code in that module means that the resulting layout will come with a static, non-semantic grid which is a thing of the past and absolutely not considered good practice anymore. In times of Sass, etc. things like that are really not necessary or recommended anymore.

In general: Layout builder UIs always result in ugly output. Of course it would be *possible* to write a tool that generates fully semantic and clean output. But noone has built such a thing yet (and I don't see that happening any time soon to be honest). Why? Because it's super simple to leverage Sass and some basic HTML to create the most flexible and powerful layout you can think of. Coding a UI for that so that the output is clean and neat, on the other hand, is more than complex. Seriously: That's a hell of a task. And I don't know a single person who would be willing to invest weeks/months in building a tool that is both nice in terms of UX and output.

Anyways... If you want to use the Layout module I guess there is nothing stopping you. Either you use Omega layouts, or you don't. You don't have to use Omega Layouts at all anyways... You can stick to plain page.tpl.php or even use Panels layouts or whatever. Omega is just a theming framework. Layouts are just a minimal, negligible feature of Omega.

Personally I go with Panels and Panels Everywhere as demonstrated in my Screencast: http://www.youtube.com/watch?v=CmTuvzbPduI&lcor

Oh but in case that wasn't clear enough: Spark and the Layout module are basically just proof of concept for toying with ideas for D8. No more, no less. It's nothing I am looking to integrate Omega with.