I think if Egypt has learned anything from the Saudi-Yemen crisis (or the Myanmar Rohingya, etc.), it's that as long as you're attacking people who are poorer than you, the international community doesn't give a fuck. The only wrinkle is that Ethiopia has a lot of Christians, so that could be problematic for Egypt. Seems like they don't really need to fight a war, though. Send a few shiny US-built missiles at the dam and problem solved a la Israel on Iraq's nascent nuclear reactor. Not like they need territorial control. Am I missing something?
I think if Ethiopia dropped a few thousand gallons of red dye in the Blue Nile they would find that Sudan is their instantaneous ally. Right now it's a water rights crisis. As soon as it becomes control of that river, Ethiopia has the advantage of gravity. I also think you will find that if Ethiopia went "Hey China" this whole exchange will become existential.
non-aligned movements, economic development, foreign bases, yeah. That's kind of the point: if you read that article they'll point out that Turkey is building bases in Egypt, too, and Libya is in a disputed civil war. So you've got Turkey/Russia, Egypt/Whoever, Ethiopia/China, US/Saudi Arabia and I mean, nobody's talked to the Janjaweed in a few years. Plus we've got water rights, oil, coffee, shipping... the region could become a veritable 7-layer dip of instability. I mean, fuckin' al-Sisi has been in office less time than Nikki Haley was. Frankly, Ethiopia is a country. You knock it over too hard and suddenly you're dealing with warlords. Which is already the situation to Egypt's west.