I'd say the HRE and Papacy ones are pretty similar with their gilding, they just have a different UI orientation to help you know you are immediately looking at something different. The Mandate of Heaven one is more unique with the Dragons.
I think they are saving UI adjustments until last, but I hope they do inject a ton of style into them. I think the art they've produced is good, it's more about stylization at this point. I think the emphasis on browns is superior to their earlier emphasis on blues (which had a very minimalist modern feel), but I'd love to see more embellishments of silver and gold in general, but especially on big weighty systems.
The HRE and Papacy and Mandate of Heaven could all be given a lot of nice stylizations to fit in their theme. The Mandate of Heaven with some classic chinese flair, the Papacy with some renaissance stylings, and the HRE with maybe some medieval gothic motifs.