Dan is planning to implement more transitions into Shotcut this year. But it requires quite a bit of coding to be done, so there could be some delay before they are released.
In the meantime I have created a new framework called GL-Transitions to make use of the transition code shown on the gl-transitions.com website. A full explanation of how to use this framework is given in the GL-Transitions area on my website at www.elusien.co.uk/shotcut.
You can very easily preview transitions, tailor the parameters to fit your requirements and create a very simple Overlay HTML filter to apply to a shotcut transition between two clips.
Below is a short video showing the use of five of the transitions, including the Inverted Page Curl, where a faint outline of the first video is shown on the reverse of the page being turned and the Cube, which rotates and the transition is reflected on the dark “floor” on which the cube rests.