So I am not sure about the real situation. Maybe somebody from Egypt here that can tell us more about this risk where he is referring too? And beside in 5 year there can happen a lot in this region.
That would be my major concern. The geopolitics of the region and the ousting of the previous elected government of Morsi (love them or hate them). Plus the 40% drop in Suez canal traffic due to Houthi attacks means less revenue for government and it may never come back as the Northern route which may open up may kill the need for the suez canal as its a shorter route. Egypt would need to show me they have a solid economic plan for the future for me to invest in real estate in their new capital.
it's extremely hard for us to get money out of here, banks have very strict rules about what money can flow out, perhaps it's different for foreign non-citizens, you should make your due diligence in any case, make sure you can get your money out of there when you decide.
and, honestly, the city is still a ghost city, I was just passing by recently.