I think it's going to be a bloodbath when the novelty starts to wear off and cheap fares fail to attract.
There will be declines in profits, followed by declines in service levels. Some of those carriers, now riding the crest of the wave, are going to have difficulty financing fleet renewals and growth. Political stability, or lack of, is going to cause passengers to think twice about using ME routes, and a lot of people are realising that living in the ME is not a glamour posting, it's moving slowly to the other end of the spectrum, a hardship posting. It will become increasingly difficult for the ME carriers to attract top management and for that matter flight deck and CC too. We only have to look at the rumbles of discontent expressed on Pprune to see this, although they may only represent a minority view, it's one that is growing.
Passengers will resist the increased journey times which travelling via the ME entails on some routes, and the unpleasant transit conditions at the hub airports. I know a lot of people, both in a personal and professional capacity, who have been loyal ME carrier supporters for several years and are moving back to other routes particularly as some European carriers offer competitive fares on connecting routes, so whilst a LON-BKK may not be cheaper than a ME carrier, a MAN-AMS-BKK might be.
Emirates was the first to expand and become overwhelmingly successful. Others followed and became successful to varying degrees but this is probably not sustainable as longer established carriers from other parts of the world will rethink their strategies and fight back against the upstarts.
Also, as jabird says, the ME carriers will not always benefit from friendly tax regimes.
Whilst I don't exactly expect the sandpit to become the next aircraft graveyard, I do think there is going to be some significant shrinkage and I can see the transit halls at DXB, for example, starting to resemble that massive echoing mausoleum which is T4 at Madrid.