4 years would be an unusually short production run for a dCS product. I would guess that on dCS’ past record that suggests up to another 3-4 years before it is replaced. Vivaldi as flagship ( now 7-8 years old) will no doubt be the first to replaced. When that happens dCS’ manufacturing capacity will be skewed for some time towards serving the demand created which is one reason why it takes years for them to work through replacing all of the lines. They are not Sony or Matsushita. Another example: Debussy came out in 2011 and was replaced by Bartok as the entry level DAC in 2019, 8 years later.
One further thought. When it happens will the Rossini replacement feature a CD drive? Is there the market demand for one in today’s environment where streaming is king? IMO there is no guarantee that such a drive will be offered as part of a one box product.
If I was in your position I would go for that offer from your dealer unless you want a long wait.