It's less likely for the Durans & Bob Dylan, as both have completed tours Uk/Ireland & Europe in the last few months.
The Coronas are likely allright and quincy k could be spot on with New Order also, they are touring around Europe in May/June. c'mere might also be on the money with Noel Gallagher, theres gaps in his schedule to play the marquee. Happy Mondays ? I dunno, would they fill the marquee ?
Van Halen are touring till the end of June in the U.S. so a trip to Europe would not be out of the question.
Elton John is playing Belfast in early June, so in with a shout.
Black Sabbath are also touring this year, Iron Maiden are planning some touring also.
Finally, a personal favourite - Neil Young & Crazy Horse should be back on tour this year.
I know country isn't that popular for the Marquee but Lady Antebellum are playing Dublin in July - they have a couple of dates free on their tour.
There is a market for everything and anything at the Marquee, as has been demonstrated over the years. They usually have a rap act or two, a teen act or two and while country music has probably been under represented at the Marquee, there has been appearances by Kenny Rodgers, Dolly Parton and Dwight Yoakam at the tent.