Nijmegen is a park, not a stadium, so unlikely they'll be playing there on a weekday, too disruptive for the people who live in Nijmegen. I'm hoping for 22nd June, as Rammstein are also playing the Netherlands the 25th, so could kill two birds with one stone. Also, my sister loves Muse too and it's her birthday on the 22nd.
That weekend seems likely to me as Bon Jovi play there the weekend before, so for setting-up purposes it makes sense. Fingers crossed...
The weekend of the 28th June is also Glastonbury, with them playing Rock Werchter on the Monday they could be headliners at Glastonbury the Friday or Saturday before.