All of the features of 2.3.5 are supported with newer versions of GP/PARI, except for iterators (sum() etc.).  For iterators
with one variable (so: all except matrix()) there is a (temporary?) workaround: use a sub with an arg, as in:
    sum($x,0,12, sub ($) {my $x = CORE::shift; $x^2})	# The first $x is ignored
(In particular, "supported" means that the tests seem to pass with 2.13.4 (except 11 subtests in t/00_Pari.t failing due to a need
for the trick above).  So if you do not need advanced plotting and are ready to use the [temporary?] workaround above, one can
probaby use the newer version.)

In addition to this, the following constructs are NOT TESTED by the test engine on newer GP/PARI
  matrix
  |var<-
  System-specific graphic (at least not on windows???)
  .methods
  nfisincl
  eval						(Signature "C" unsupported)
  lexical variables are not special-cased	(Is there a need???)
  [row,]
  most of default()s
(and maybe some others too — especially with unsupported signatures!).
