I read a suggestion for a wait x milliseconds action somewhere, and I was going to second it, but I can't find it.
I think two wait actions would be nice. One would be applied to objects (to, say, freeze the player for 2 seconds), and the other is a global wait (not sure what that would be used for, but lots of things have them, and it must be useful for something). But the first wait is far more interesting - you could use it to stop all processing on an object, say for a cutscene or something (I know it's possible to disable input and collisions manually, but it would be much cleaner if there was an action to "remove an object from processing" for a little while.)
Also, I gotta say that this is a totally awesome engine, and I'm really glad that you're letting us use it for free. I should upload my first game in a week or so (incidentally, does anyone know a good guide to using functions in Construct?)