I want to make a bet that till 2020 ( give or take 1 year
p ) one of these two will host, even if we keep the topic dead for a while, let's see if I get it right in the future.
2018 should be chosen next spring before the 2016 finals take place. There are valuable candidates but the rules are much lighter than for EL and CL finals.
Both stadiums will perfectly qualify to host a UEFA Supercup, but our smart ass FRF guys should think of informing UEFA about them since they are perfect candidates for the game. Since leaving Monaco Louis II ( 18.500 ) the UEFA Supercup has taken place on stadiums located in places less likely to be able to host another type of final or in places usually ignored ( such as Wales, as Millenium could've hosted a CL final anytime since it was built but UEFA chose Glasgow, Manchester or London in Britain and now will finally do ).
2013: Eden Arena, Prague ( 21,000 )
2014: City Stadium, Cardiff ( 33,000 ) -Just streets away from Millennium, where the 2017 CL final will take place
2015: Dinamo Arena, Tbilisi ( 54,000 ) - This one could've hosted an EL Final
2016: Lerkendal Stadion, Trondheim (28,500 ) - Norway stronk
2017: Philip II Arena, Skopje ( 33,000 )
The Craiova stadium will probably be able to host anything from 2018 even if it's not yet built:
Cluj Arena is 30,200, built in 2011 funded just like Craiova by public funding and unfortunately it has a pretty useless athletics track ( they could've built a small arena with a few seats somewhere for this as the interest for these events is 0 ).
Cluj is also considered the top Romanian City in terms of Quality of Life average, for 2015 is in Europe the 29th ( above Paris, London, Barcelona, Lisbon, Budapest or Milan, the top 10 being: Zurich, Frankfurt, Edinburgh, Trondheim, Geneva, Vienna, Copenhagen, Stockholm, Berlin and Trieste ). In Romania, only Brasov was also in Top 50 and Bucharest is marginally outside this top.
Craiova on the other hand is, from the big cities, a much less lovable place, but in terms of football it was the first to have a team in the final phases of European competitions, was considered up until 10 years ago the 3rd most supported team ( more likely 4th after the Big 3 from Bucharest ) and even if it was named "The city of hunger" before 1989 now it's at an acceptable non-3rd world level.
The stadium will be 100% made for football and it can be a valid candidate, another advantage is that it has political support for it as Cluj is leaded by the opposition and it's closer to Bucharest if this would matter.
The press hasn't been talking about this at all because they usually take 10-15 years to realize in what world they live, but we all know it's perfectly plausible thing to write about since after all Bucharest will get some matches for Euro 2020 while the others only other chance would be if Romania would co-host a Euro, in which case, they would both need a 3.000-5.000 seat upgrade to get the group stage matches slot and is highly unlikely to happen soon.
FRF only has to propose as it's not that hard, easier than before when Bucharest got the 2012 Europa League way before the stadium and was a much bigger project.