Its interesting that Turkish government officals have not simply outright rejected the idea. In fact, the only response seems to be ignoring the proposal.
Realistically, the best outcome one can hope for with the S-400s is that a former Soviet republic in Central Asia purchases them (more likely to be approved by the Russians). It seems like Russia has had great success in causing division with the sale.
Its either:
1) continue to 'upset' the US by holding them = No F-35s + Embargo and Russian cooperation e.g. Akkuyu continues
2) Cooperate with the US e.g. stored in a secure location without the ability to activate the system, then both parties can analyse the system = F-35s + lifting of embargo + perhaps more favourable relations e.g. less criticism of 'actions' in the East Med. However, this option would undoubtedly severe relations with the Russians - one can expect a number of sanctions (gas, oil, tourists) and the suspension of the nuclear powerplant.
This outcome would be largely similar if the S-400s were supplied to Ukraine, however ontop of this, Turkey would give up its role as a mediator.
3) S-400s remain in the current state, Siper and national projects advance to a stage where the S-400 is no longer needed. S-400s are then sold on to a nation 'friendly' with Russia, and other cooperative projects such as Akkuyu continue.
