As I understand, truncate-lines is a buffer property, so it applies to
every line in the buffer.

Is it possible with some rather small changes to redisplay make it per
newline property, so you can specify which line to truncate and to which
apply buffer setting?

Here is the example:

(setq truncate-lines nil)
(insert "<very long line>"
          (propertize "\n" 'truncate-lines t))   ; this line will be
truncated
(insert "<another very long line>" "\n")    ; this line will be wrapped

What do you think about this feature?

-- 
lg