I don't really know what to think about the whole Leliana-disguised-as-Envy-seducing-you cut content, but it would've been very interesting to see what would've happened to the relationship between the Inquisitor and Leliana if Quizzy decided to tell Lels that they slept with her.
I can only imagine how much devastated Leliana would be (especially if you consider what happened to her in that prison in Leliana's Song) to find out that the Inquisitor used her in a way, even if it was only for pleasure.
I, as a player, would have probably been put off playing and interacting with Leliana for the rest of the game, most likely restart to do In Hushed Whispers (which, in my opinion, is the most amazing moment of Leliana as a character). 
Except that it wouldn't have been her per say. In the scenario Envy took her form, but the real Leliana was untouched. She still would find it disturbing, but the squick factor would have been diminished by the fact that the Inquisitor thought she was making a move.
I can imagine DAI Leliana would have reacted to such a revelation with a mix of disgust, anger and possibly scorn. She certainly wouldn't think too highly of a Herald who got fooled by any demon, and after learning about this particular type from Cullen, she would think even less of them.
f anything it would have been interesting if internal politics had played a bigger role. We get elected as Inquisitor unanimously by the 'Council of Four' (Cullen, Leliana, Josephine and Cassandra), but what if the vote had been divided? What if we'd been installed as a mere figurehead for politics' sake and we'd had to actually earn the respect and trust of our inner circle?
As it is, the approval/disapproval mechanic is largely cosmetic. Most of the companions' personal quests unlock regardless of how they feel about us. Higher relationship values could have lead to new abilities or perhaps a buff like in Origins.