Because M15 spoilers.
The comeback of Convoke makes Theros' Inspired mechanic a lot better. Or rather turns it from something unreliable into something much more reliable, especially now that convoke will be appearing in all colours.
Preeminent Captain, Raise The Alarm and Obelisk Of Urd combined with the ton of good white creatures that are soldiers already (Brimaz and such) Soldier tribal might be a thing, especially with heroic, launch the fleet and the new Ajani. Maybe White with a splash of blue for countermagic and things like Military Intelligence, Ordeal Of Thassa and the new white 2 drop 2/1 that gets +1/+1 if you control an island and has 3U: tap target creature.
The souls are pretty interesting as well, Soul of New Phyrexia giving any deck a possible 6/6 trampler with upsides for 6 and the Soul Of Theros can completely take over a game in no time if you have a couple of creatures.
The New Nissa and Garruk are pretty sweet as well, Nissa's +1 almost makes her cast only 1 mana and the new Garruk could be worthwhile in a green devotion/ramp deck that can afford to pay 7 mana easily and early.