But, from a variety standpoint, we could use the Dornier, but not the 217. If we're going to get the Dornier, it will most likely be the Do-17z for EW arena.
Actually the Do 217 could fill a huge gap in the planeset. The 17Z would only see use in EW (and even there not much, being massively outperformed by all other buffs) and occasional special events.
The Do 217 could be easily used in EW, MW and LW, as well as special events (Dieppe, Normandy, MTO (sinking of the Roma).
Don't forget that there are no really competitive axis buffs in LW, if you have a German Iron squad you have to stick to a very slow and almost defensless bomber.