This is a nightmare to try and keep up with, purely because there is no announcement from ForgeWorld that this is happening / has happened / is going to happen. The Rhino doors are a bit of a surprise because we went through a mini-purge (mini as in 'small', not 'model') before Covid shut everything down, but I suppose they're looking at prioritising Rhino Deimos for 30k. I did think that maybe they would be prioritising Repulsor sized doors for 40k, instead of traditional Rhino chassis chapter doors, but even the new Repulsor doors have gone (only the Blood Angels one is left, probably because they still have stock, but when they're gone they're gone).
It's hard to predict what is going to stay and what isn't. I was sure a while ago that generic Rhino doors would stay, despite the fact that Land Raider doors had been culled, and I have been proved wrong. I still think FW's plan is to have a single shoulder pad variant (MkIII or MkIV), head and Deimos door upgrade per Legion but I'm struggling to see why Deimos pattern would stay if the regular Rhino pattern has now gone. Plastic Rhino vehicles are cheaper than their FW resin Deimos counterparts and are still 30k accurate as well as default in 40k.
For those really wanting to do some deep investigative work, it's interesting to see the comparison between the UK and US versions of the site (you will have to change the shipping location to see the difference) as North America has it's own stock, and some items won't go "No Longer Available" until the corresponding warehouse location is out of stock - even FW aren't silly enough to stop selling products they have on their shelves! As a for instance, in the US you can still purchase Death Guard MkIV shoulder pads, whereas the UK stock has now gone NLA. It's a case of picking through and seeing what is (and isn't) there.
The most annoying thing is not knowing that something is gone until you try to search for it and buy it. I just paranoidly checked a kit that I do buy sometimes, the 40k Khorne Terminator and PA upgrade packs, and the Terminator is NLA with the PA down as Temporarily Unavailable. Lord Zhufor is still available, but who knows for how long - and not knowing whether an item is on the chopping block until it's gone is stressful.