The most likely qualification setup for EURO 2016 (and beyond) is a 9-group system. I'm going to look only at the one host scenario (France), but it makes little difference when you move to two hosts.
9 groups (2 x 5, 7 x 6)
Top two from each group and the best team in third place advance. The other eight play-off for the final four spots.
Using the current UEFA coefficient these would be the pots for the preliminary draw:
Pot 1: Spain, Germany, Italy, Netherlands, Croatia, England, Portugal, Greece, Turkey
Pot 2: Sweden, Russia, Czech Republic, Romania, Poland, Israel, Ukraine, Scotland, Denmark
Pot 3: Switzerland, Serbia, Bulgaria, Norway, Ireland, Slovakia, Finland, Austria, Lithuania
Pot 4: Belgium, Northern Ireland, Bosnia-Herzegovina, Wales, Latvia, Macedonia, Slovenia, Belarus, Albania
Pot 5: Hungary, Cyprus, Georgia, Moldova, Estonia, Kazakhstan, Armenia, Iceland, Liechtenstein
Pot 6: Azerbaijan, Montenegro, Malta, Luxembourg, Andorra, Faroe Islands, San Marino
Group 1: Croatia, Russia, Norway, Bosnia-Herzegovina, Georgia, Azerbaijan
Group 2: Netherlands, Sweden, Finland, Northern Ireland, Kazakhstan, Faroe Islands
Group 3: England, Czech Republic, Serbia, Belgium, Armenia, San Marino
Group 4: Germany, Israel, Austria, Wales, Iceland, Luxembourg
Group 5: Greece, Scotland, Lithuania, Slovenia, Cyprus, Montenegro
Group 6: Portugal, Romania, Ireland, Latvia, Hungary, Andorra
Group 7: Spain, Poland, Switzerland, Macedonia, Moldova, Malta
Group 8: Italy, Denmark, Bulgaria, Albania, Estonia
Group 9: Turkey, Ukraine, Slovakia, Belarus, Liechtenstein
Remember, top two from each group and the best team in third place advance. The other eight play-off for the final four spots.
What big gun could fail to qualify if third place means you're still in the race?
With second place enough to avoid play-offs, qualification will be achieved sooner and teams will play their last matches with their second string. How will this make the qualifying more competitive?