I also like how smooth and fluid the animations are (the fact they aren't just statues until they attack, such is the advantage of pre-renders...maybe they aren't just a naff thing we all remember from the mid-90s) and the music sounds like a good upgrade while being familiar. Still I find it odd they've leaned more toward FE3 in terms of music (especilly the player phase theme...I much prefer the FE1 version) but gameplay leans more toward FE1 (though balanced and hopefully lacking things nobody could ever figure out like boots killing promotion movement boosts if used before promotion).
Along with the fact that the video depicts a Social Knight stabbing an enemy with sword whilst mounted, it'd be a wonder at all for a reason to dismount.
There is a simple reason to dismount. You'll laugh at it. Horse Killers (and equivilents, still must be a handful of enemies with these weapons). They won't get effective bonuses if you dismount...I was going to cite that as the FE4 reason except the fact the only unit who can dismount (Celice) is immune to those anyway (thanks to Awareness)
Of course Pegasus Knights have bigger reason to dismount with Arrows
and in FE3 book 2 is the key to getting the Lady Sword nice and easy.
