I have several issues with the SwiftKey themes:
1. There are lots of themes, but most of them feature the exact same key layout with another background. These 'themes' should not be listed as separate themes, but as variations of a theme. The most sensible thing to do to get some structure in this mess, is creating several keyboard layouts (i.e. with rectangular keys, rounded corners, no border,...), then let the user choose whether or not to display secondary symbols on the keys, and then offer color options.
2. There is no reason to put the SwiftKey logo in plain sight on the spacebar. I know which keyboard I'm using, and I 'm happy to tell other people if they ask, but I don't want your logo all the time in my sight. Put it in the '+'-menu if you absolutely need to show it somewhere.
3. There are almost no beautiful themes. I know this is very subjective, and yes, there are themes with balloons and fireworks as background images, and I can even use a custom photo,... But to me, a perfect keyboard is the keyboard that is not "in your face"; it's a keyboard that you don't even notice using. It should be clean, and have no showy interface elements. These themes are (almost) not available to choose from. The only theme that comes close to this, is 'Minimal material light', but even in a 'minimal' theme, you couldn't stop using colors and painted the shift, backspace, enter, emoji and symbols keys lilac.
Please get rid of the nineties keyboard layouts and introduce some modern ones, and make them fully customizable.