I concur. I expect Russia to test a nuke in Siberia in a month or so. Just to see the reaction and to show their resolution. And If the Ukrainian advancements continue, they will use a tactical nuke in a location where the death toll won't exceed a few thousand. I cannot guess what will happen after that. It depends on the World's reaction, as you said. Things can escalate very quickly. I'm not so sure of it but my gut feeling tells me that Russia won't get nuked. I don't think any country in the World, including the US, will risk to be decimated by hundreds of nukes for the sake of Ukraine.
This war frightens me. Putin has cornered himself and Russia so badly that he might just say "f**k it" and start pushing the red buttons. If it comes to that, I hope his subordinates will refuse and put a bullet in the right place.
A dog that barks a lot doesn't bite. Putin built himself an image of a ruthless strongman without any opposition to him but deep inside he is a coward that is full of insecurities. He is afraid and paranoid even from those around him and much of his actions talk about this.
Even if he gives an order for a nuclear strike it doesn't mean that it will be carried out. Usually there is no such thing as a red button but we talk about multiple people on different levels of command that must all give their okay about it. I doubt that many people out there are ready for a nuclear war and a total destruction... especially when all the kids, wives, bank accounts and mansions of the Russian elite are in the West. Why commit a "suicide" for some crazy old man that will probably be dead soon anyway. I won't be surprised if the minute Putin even dares to order a nuclear strike he would probably be killed or couped.
Though these are my thoughts as a sane and relatively pragmatic person... Yet as we see sanity is hard to find in most Russian heads in general so I might as well be wrong too.