Jon de la Vega on his Github project page:

I like the look of Omnifocus 2 but it’s not ready for everyday use so I decided to make a theme for OF1 with the renewed look.

I’ve had access to the OmniFocus 2 “private test” for about a month, but right now it’s not usable on a daily basis (for me, at least). This theme really dresses OF1 up like OF2 in a way that is, surprisingly, nice. If you want to get a feel for where Omni is taking the design but retain the functionality you’re used to, this theme works quite nicely.