As seen by loading Compiler, then filing in any new-syntax file, it doesn't support it.

With the highly trivial smalltalk--backstage--2.2--patch-64 "support new syntax with STInST compiler", this now works. I also verified that the STInST compiler is actually being used by ensuring that Presource works with no changes, as it does.

Example:

st> ('a' =~ '(?i:A)') inspect!
An instance of Kernel.FailedMatchRegexResults