The Wildcard move in this is Ukraine advancing south from Kherson over the Dneiper and racing for Crimea in lightning blitz. Everyone discounts this because everyone says it cannot be done. Much like the Incheon landings in the Korean War.
I'm going to TL;DR this very heavy, you've taken the "Pro" so I'm going focus mostly on the "con", but it is not impossible.
Firstly, if Ukraine had sea-born landing capability anymore, this would be a possibly. You could very probably get a mechanize company on the shore and use that as flanking support to support any river crossing. But they don't, they have been doing small teams of marines as a nose-thumbing to demonstrate Russian weakness, but those teams cannot stay or hold territory. If you already have the territory and are pushing south, you could use raft/small boats to bring down infantry to support, but those infantry will need vehicles that wouldn't be raftable.
But as it stands, Ukraine has one option (edit: if they want to go south into Kherson oblast): Over the Dnieper. This is not the world's craziest river, but it is wide enough at Kherson you'd need dedicated bridging - pontoons or (ideally) preformed structures you can drop into place. Scissor-bridges wouldn't be an option. I am not an hydro engineer but I don't think you could get across with a single free-formed span and expect it to hold under military loads, and that's to say nothing of the equipment that would be needed to move it.
What I'm saying here is there would be very long, very large segments of pre-fabbed bridge. This would be very difficult to hide - I live in a city that did pre-prepared bridge replacements for a corridor, and for just crossing highways on already prepared placements with no one shooting at them, it was a huge undertaking with a full year of prep and very visible heavy equipment. You couldn't do that shit quietly.
The front has also learned full in to the WWI recreationist mindset- there is no smash and grab. Ukraine needs to be ready to take, hold, and supply. Russia, even given everything, still has tube and range superiority. Any bridge you put in place you MUST secure a 50km+ bridgehead ditty mao or you will quickly be doing the Ukrainian version of the humiliating withdraw from Kherson because your bridge will be underfire. And the more field expedient your bridge is, the less able it is to take fire.
Russia had control of Kherson, and was using a pontoon bridge. Do you think that was their first choice?
If you want to reverse roles/positions and it was Russia looking to cross, Russia might be willing to get some sort of crossable structure down, then throw a bunch of mobliks and T-55's into the grinder to see if they can do anything good; if the do, great. If they don't and the bridge gets destroyed and they are cut off, oh well you're out some mobliks and T-55s. But Ukraine can not risk their armor getting stranded with no evac. And right now the evac plan for the bridge being knocked out would be "drive through the entire Kherson Oblast to Orikhiv".
You could possibly try to do some gayops by doing a version of the 2022 rope-dope where you have some bridging equipment that looks like its ready to drop new bridges, and move extra brigades too look like they'll be using them, but Ukraine very clearly wants to cut Crimea with their 2023 counter offensive, so getting Russia to deploy extra troops that would be expecting action, to the Southern front would not be very productive.
Extreme extra tl;dr:
Bridging the Dnieper would require masses of contruction equipment or water craft, as well as troops, we are not seeing, and Russia would definitely observe and respond to. Its not IMPOSSIBLE they have 3-4 preformed bridges poured in Kiev that will get overnighted to the front but that's not what my money would be on.
A Dnieper crossing would be something that might be done to supply or reinforce an already successful attack elsewhere but it is extremely high-risk and I don't think they'd try.
I trust that guy about as much as I trust the Russian MOD releases.