This is an amazing app, more fast than others. Just add more features like customize colors (like iTerm2), transparency, dropbox sync, and a iOS version.
Core Shell can be the "Sublime Text" of SSH clients.
The appearance and color scheme customization is nice. But at present, our major focus is on features that make professionals doing their daily work more efficiently. With the next version (which is version 1.6), you can download / upload files over a shell window, that's impossible on most of terminal emulators.
dropbox sync
That is already supported. You can specify the Core Shell syncs with a folder that is enclosed in Dropbox local folder.
I use 1Password 6 with Dropbox sync, it syncs with a folder inside Dropbox's sync folder:
".opvault" is a folder not a file. 1Password lets you locate Dropbox's sync folder much faster, there is no different from "Sync with Folder".
Believe me, color scheme customization will be a good point because just iTerm2 have this feature.
What color scheme that Core Shell lacks but you'd like to use?
Termius has a good interface too but is too slow.
AFAIK, Termius is not a native macOS app, it's developed with Javascript / CSS and running inside a web container, that’s normal if you feel it's slow.
The future version (1.7 or later) of Core Shell will provide basic support for color customization, but in a different way. It won't provide a palette interface as in Terminal.app or iTerm2, but will gain the ability to load profiles exported from them.