Dynamis cant be istanced like MMM, because MMM isnt istanced too. the MMM map is like a bigger map composed by the same mini-map repeated 4-5 times. every times someone enter MMM it is placed in one of this mini-map until all the mini-map are occupied and the zone is considered full.

you cant have dynamis works like this because of the map dymension and number of map zone actually free to use.
they will have to totally rework how the map system currently works to do this.

said that...we all hope they do something cool...lets wait till they reveal more juicy details