To everyone who wants to play the game right now and can't wait until the official version is published:
Get yourself an image viewer that can convert WebP files to JPG. My choice is the latest version of Faststone image viewer. The following instructions are for this tool. Start Faststone and choose 'Tools' in the menu. In the drop down menu choose the batch convert option (or press F3). Open the Dominion 'images' folder ( in the 'game' folder).
Click on 'Add All'. Choose JPG as Output Format, then uncheck the output folder, this will convert the images where you want them. The only option that needs to be checked is 'keep original / date time', but you can also check 'display error messages' in case something goes wrong. Now click on 'Convert' in the lower right corner.
It will take 5 - 10 Minutes depending on your gear. It should be clear that this will increase the file size of the game, but now you can play this Beta version. Happy gaming.