I've always thought this would be much less useful than people think. Consider typing "On collision between SpriteA and SpriteB". If you typo'd and wrote "On collisiion between SpriteA and SpriteB" Construct wouldn't be able to recognise the condition and would point to it as an error. And it'd take so long to type out you probably could have picked it out from the menu by then, if you're experienced. Plus the text format could never be as clear as the event sheet: to prevent ambiguities in which part of a condition or action are parameters, you'd have to differentiate it somehow. So instead of "Sprite value 'X' less than 5" you'd have to type something like "Sprite: value param('x') param('less than') param(5)" which has already destroyed the readability.
Are you sure it would make it quicker and easier considering that? I think an experienced user can click through the menus very quickly so typing out a long event could actually take a lot longer IMO, especially if you make some typos.