I don't think the effect on Trad residuals is at all predictable, and many people won't go CX because of the cost.
So I agree with Ian…….a well cared for 3.0Roadster for under £40k is a bargain (for example).
There are so few Trads around, and the demand which has sustained for Trads won't suddenly evaporate overnight.
Here's some man maths from around 2012...…..when the 3.7 Roadster was announced, I thought this is the car for me...…...

But then looking at the costs......I would have needed almost £30k on top of my S1 Roadster to do the deal. It made more sense (haha) to put that £30 into a Plus 4, and enjoy two Trads.
The CX is the same logic but the reverse. I could trade both my Trads, and get a CX. I then have one Morgan I can't mess with very much, and for me that's not how I like my cars. That's the reason I never bothered with a Boxster/Mx5/Z4 and so on.