I see no progress between 2020.1 and 2020.2 so I’m wondering: is GPU progressive abandoned?
no
It isn’t abandoned, quite the contrary. We are focusing on fixing bugs at the moment, then we will go back to the remaining work needed to bring the GPU lightmapper out of preview.
Good, take your time though: I just bought The Bakery 
Can you state the difference from your experience?
- It’s like driving a Bobcat. It works reliably in all scenarios and gets stuff done and requires dexterity.
- it is fast if you have an RTX 2060
- you can log issues on Github and every week they get answered or fixed by Mr. F
- When you buy the RT module you get true real time preview, it changed my life as an artist!
- you have granular control over how probe are baked: Unity legacy which maintains a nice smooth darks or the beautifully saturated L1 that crushes darks
- you have granular control over how normals and direction are baked in, from unity’s own method to more exotic stuff like MNR or SH. I chose full bake which looks so cozy and is mobile friendly.
- leaks can be controled by using certain techniques
- choice between two noise reduction and atlasing
- Very well documented by someone who is passionate about good looking lightmaps, every answer is in there
(Edited out the 2 minus as they were both fixed by Mr. F)