My understanding is that the UK Government are still committed to giving the GAA the same amount of money that was on the table when Windsor Park and Ravenhill were renovated, but the costs of building a new ground to UEFA specifications would be far higher than building a groundnsuitable for County Antrim board (hospitality, media etc etc).
The reason it wasn't built initially was due to the local residents objecting and health and safety issues as all fans would be having to leave onto the Andersonstown Road, whereas both Ravenhill and Windsor have three or more exits from the ground.
I'm not in the slightest concerned about one game in the Euro's not being played in Belfast as I feel the cost far exceeds any benefit (even if it was a game between two countries with large travelling fanbases, it would only host one football game and would be a stadium either not best suited for Gaelic games or not suitable for football (I think the GAA pitch length is 20 meters longer than maximum for football).
If a walkway could be built from Kenneday Way to take fans from the M1 end of the ground, it would help, not sure about the height stands could be built without breaking legislation concerning local housing, but it could be redeveloped suitable for Gaelic games for a lot less than needed for UEFA (10,000 capacity Terrace at the Andytown road and M1 ends, 10,000 capacity stand on the Twinbrook side off the ground with media, hospitality boardrooms etc and on the city side of the ground a 7,500 stand with hospitality etc and 5,000 terrace below it for a fraction of the price UEFA would require.
Still leaves the issue of congestion, Boucher Road playing fields for cars and buses on the industrial estate would be possible, but that area is a nightmare traffic wise without a game on, about a two mile walk from the new grand central train station or Balmoral halt and the Glider is much worse than the trams in Manchester