They should have done this ages ago. We may well have avoided the disaster that became Gordias. All they need is a bare bones assets and concepts they want feedback on. Take, for example, the change to ejection mechanics. Have players test out just that portion of Sophia EX and get a feel for whether they think it's too easy or an improvement over Titan and Sephirot. Another example is tuning. They could use existing mechanics or fights, thereby avoiding any spoilers to new fights themselves, and simply scale the damage to what they think the scaling should be. Had they done this with Gordias, people would have been quick to point out it's far too high.

Small things like that could go a long way to improving the overall game and avoiding mishaps like Gordias, Zurvan and White Mage's current design. The devs are only human after all. Mistakes and miscalculations happen.