I would add in PvP as well for the salt in the soup. :-)

Like 4 man Coliseum

Round 1 PvE
Round 2 PvP
Round 3 PvE
Round 4 PvP
Round 5 PvE
and so on.

For entering Coliseum it is mandatory to form a group of Tank, Heal, DD, DD.
During Coliseum it will NOT be possible to change the chosen class.