It could be an incredible idea! But in this case, it will create a new block against Russia (except Belarus if Lukachenko stays and also Turkey which is playing on both side) and Putin, this chess player, will never let this happen!
Second point, for me, Turkey is mostly interested by Western Europe, not Eastern so this kind of block is not in its interest.
They will be suffering from economic downturn when this Union happens because this could mean that the countries that will join this union will have to exit in EU and I am pretty sure that EU will retaliate through economic embargo to some of those countries.