max_execution_time - ITIMER_REAL vs ITIMER_PROF

I'm interested in having a timeout that corresponds to clock time as
opposed to PHP execution time (the current behavior of
max_execution_time). A cursory scan of the source implies that (on
Unix at least) something that behaves like zend_set_timeout() but uses
setitimer()'s ITIMER_REAL timer instead of ITIMER_PROF would do the
trick. Before I investigate much further, a few questions:

• Is anyone aware of a reason why ITIMER_REAL would cause problems?
  (Signal delivered while PHP is doing something uninterruptable?)
• Assuming ITIMER_REAL works OK, is there interest in incorporating a
  patch for a "max_real_time" config directive / timeout?

Thanks,
David