There probably won't be a cross-platform UI layer and many Apple frameworks won't work, although apparently the Foundation Swift rewrite already works. For a lot of companies though, simply being able to share business logic will be a big plus. At my current company we have a lot of talented Swift people and existing code written in the language so being able to share anything would be a huge advantage.

I'm biased but I personnaly find the language really productive to work with, runs fast enough for my needs and let's me target more and more platforms.