Solaris 2020 have landed and I've been listening and comparing back and forth with my OG Solaris, so thought I'd share some VERY preliminary thoughts. I've had my OG Solaris since it was released, so it is well broken in, whereas the Solaris 2020 has only about five hours of use now, so these should be taken with a grain of salt, particularly relative to the low end given that the 10mm ADLC dynamic driver definitely needs to be run for a while before it really opens up. I've been using both with PW Audio limited cable (I have two), out of my SP1000M, so beyond the Solaris 2020 being brand new, the comparison is pretty apples to apples.
First, a note on ergonomics and size of the new 2020s. Campfire has said they shrunk the size by 20%, and while that doesn't sound like much, in person this feels much more significant. They feel a lot smaller. They nestle much more closely in the ears, and although I never had a problem with the original Solaris' fit, the 2020's smaller size definitely makes them feel more flush with your ears and less like you have bolts sticking out of them. However, something to note is that the housing is not only smaller, the angles at which the sound tube upon which the tips fit has changed slightly and the sound tube itself sticks out less far from the rest of the housing. So overall, at least on my ears, the Solaris 2020 do not fit any deeper in my ears than the OGs (in fact, it may be possible for me to get the OGs slightly deeper in my ears than the Solaris 2020s). The 2020s are overall have the edge in comfort even though the OGs never caused me any fit issues. Two other things to note about the physical appearance are: 1) while that the new PVD finish is very nice and I like how understated it is, it has a glossy finish as opposed to the more satin finish on the OG, which definitely makes finger prints and oil from your fingers more noticeable, and 2) it looks like the vent on the 2020s is slightly larger than on the OGs--I'm not sure if this makes any sonic difference, but it is something I noticed. I haven't taken any pictures yet, but will upload some once I do.
Ok, on to what you probably care most about--some sound impressions. On the whole, as it sounds like from others' descriptions was the case with the Solaris SE (which I've never heard), the 2020s are close to the OGs sound; however, there are noticeable, albeit slight differences. You still have the big soudstage, that lovely clear, holographic sound of the OG Solaris. The biggest difference, which also sounds to be in line with how folks have described the SE sound in comparison to OG, is that the mids are slightly but noticeably more forward as well as a bit fuller than the OG mids. The overall result of this is that the sound is a little more cohesive. The 2020s are still great at layering and there is great imaging and instrument separation, but whereas on the OG, different parts could feel very much like individual tracks layered on top of each other, the 2020s are a little more of a cohesive blend. Depending on your preferences, I could definitely see some people really liking this (it is more realistic), but others might prefer the slightly more distinct layers. With the slightly more forward mids and more cohesive blending, you also get a little more texture and resolution; however, the flip side of this is that on some tracks, bass and treble feel like the pop a little bit more on the OG.
Speaking of treble, on early listening, the Solaris 2020 feels perhaps a little more textured and a little bit better blended--a little more refined than on the OG. Still the same airiness and sparkle of the OG, just a little more cohesive. As far as the bass goes (and again, I really don't want to make any definitive impressions here), my early impression is there may be a bit more mid-bass on the 2020s compared to the OGs, but the bass has already changed a bit in just the first few hours of listening, so completely reserving judgement until they have been run in a bit more.
(edited to correct some typos)