For those shocked by the new interface, I found this video, which claims to be from 9 July 2009: Foldit Selection Interface.
So, no one can say the new interface arrived suddenly out of the blue. The selection interface covered in the video is of course the precursor of the "new interface".
The video briefly introduces the selection interface, but it doesn't dive deeply into detail. Back in 2009, the
action bar didn't have too many actions.
For anyone trying to get up to speed, see new interface icons for a quick look at the most common items in the action bar.
The wiki also has a page for each of the original interface menus and modes, showing where the cheese has been moved. See new interface migration for an overall view of the changes, and links to each of the detail pages.
Most of these "changes" have of course been part of Foldit for 12 years now, if we can believe that date in YouTube.
The selection interface provides a lot more than larger buttons. It is a different way of thinking about how to work on the protein. The point of it is to be able to 'select' which segments you want to work on, and then be able to perform operations on those segments.
For example, in order to reassign some set of segments a different secondary structure, in the original interface you would have to first switch to structure mode, then right click on a segment and assign the structure, then left click and drag from that residue if you need that structure to extend to other segments. In the selection interface, you simply select which residues you want changed, and then hit whatever structure you want them changed to.
As for merging them - I don't see the point. The selection interface already provides all the tools that the original interface does (or should). It is a matter of personal preference.
I guess at this point, the developers personal preferences include not constantly having to worry about how each new feature works in two similar but different interfaces.