Would this be counted as a legal S8 eviction?

I have just read about S21 been removed from law, I have the following threat from my landlord's office received earlier today.  I posted about a problem in late 2021 where I had to be quite forceful to get some repair work done and had to wait unil now to see what would happen on renewal.

To summarise.

Tenant for over 20 years. 
Dad is my guarantor. 
No missed or late rent payments. 
No anti social behaviour complaints.  Am a very quiet tenant. 

LL manager rang today, the call was in a threatening tone, I was alerted that in previous years, my Dad was crossing of my Mum's name and then sending the form back, apparently after over 20 years this is now suddenly a problem, they was straight to the point, I was informed if any of the following happens I will get a S21.
Mum's name crossed off.
Alterations to form.
Non return of form.

There was then a second conversation later which albeit was more friendly with a different manager, it was explained they think even with my payment history, its a intolerable risk to not have two guarantors, they confirmed if my Mum refuses I will get a S21, but after saying if that happens and reminding them I have the owner of the property on my contact list they decided to give a second option,  The second option was 4 months of rent in a holding account, this is not rent paid in advance but instead "on top" of rent paid.  They said they refuse council acting as guarantor when I asked why, they said they cant disclose reason, I also offered them two alternatives.

Rolling tenancy agreement, so basically they have pretty much no risk, S21 issued any time. Refused.
Six month agreement instead of 10, as this is equal risk to their 4 month deposit idea.  Refused.

It feels like they trying to extort cash out of me maybe to cover cashflow issues or something.

I am aware S21 can be issued for "any" reason, but I am curious how much the scrapping of S21 will change things.

If a landlord tried to S8 evict a tenant with 20+ years of perfect rent payments on the grounds they couldnt get a second guarantor contrary to the original agreement, would a judge laugh and say you been silly or would it be considered a valid legal reason to evict?

To clarify as it may be asked, there is no outstanding rent payments.  So the perfect record is still ongoing.

I am aware S21 can be issued for "any" reason, but I am curious how much the scrapping of S21 will change things.

This is completely irrelevant to your situation. You are talking about a future unknown and you are dealing with a current situation.

For this to happen - almost out-of-the-blue - you'd think there's an underlying reason. You may need to dig, or continue to offer things, or just sit tight and see whether they follow through. I think I might be minded to sit tight. See if they contact you again. Don't pre-empt anything. It almost seems weird that this has suddenly caused the Agent angst and you do wonder whether they're acting on behalf, and in the best of interests of, the Landlord. What Landlord wouldn't want a long-term Tenant who pays rent in full and on time? You have a direct line of communication there, hmm?

You may end up with a Section 21. Nothing can stop that from landing if it is going to be sent. If it does, we can answer more specific questions.