Welcome to the forum.
Any eta on a new Eldar codex ? I'd hate to spend time and money buiding a force up for it to be outdated next year.
The short answer to that is no. The longer answer is that there is no guarantee that a new codex would actually invalidate your force, providing it's well balanced to start with, and isn't built around one unit, so I wouldn't worry about this too much anyway
I appreciate that you're going for an Ulthwé theme here, but I think that you're overdoing it a little bit, and leaving your army rather exposed as a result, particularly regarding the infantry section.
When you only have 1500 points to play with, taking Warlocks and two Farseers eats up a lot of points. Warlocks are the most durable Eldar assault squad, but they lack a cutting edge against MEQs, so if Marines are going to be your main opposition, I'm not convinced that they will actually perform all that well. For this reason, I recommend dropping this unit (Ulthwé armies don't have to include a unit of Warlocks), and increasing the Howling Banshee squad to full size.
The Storm Guardians on foot do not look as if they are likely to achieve very much, and you badly need a mobile scoring unit in fifth edition for objective based missions in my experience, so I suggest that you mount them in the Wave Serpent vacated by your Warlocks. As far as their equipment is concerned, the tri-template combination (two Flamers and a Warlock with Destructor) is the choice for an anti-infantry unit, while the anti-tank squad (two Fusion Guns and a Warlock with a Singing Spear) can be useful, particularly if you don't want to take Fire Dragons.
Speaking of Fire Dragons, a third Wave Serpent transporting a unit of these Aspect Warriors could come in useful. Taking only two Wave Serpents in a 1500 point list is marginal in my experience, particularly if facing Marine armies with a high number of heavy weapons, so you may wish to consider adding a third Serpent to strengthen your mechanised wing.
The Guardians and War Walkers are excellent choices, and give you plenty of firepower, but you're going to need to defend them from assaults and close range attacks. A squad of Striking Scorpions would work well for this in my experience.
The sole Wraithlord doesn't add much in my opinion, so unless you want to take two of these and use them for anti-tank duty, I suggest dropping this, and spending those points elsewhere.
As for the additional units you were talking about, Dark Reapers are expensive and static, so I don't recommend those, Harlequins don't fit the Ulthwé theme, and you don't need Eldrad to field a successful mixed Eldar list in my opinion.
Finally, I'm not convinced that taking two Farseers is necessary. I suggest that you add Runes of Warding to the second one, and drop the first altogether to save some points.
Overall, the core of this list is solid, but I just feel that it needs to be slightly stronger in all departments, and you can bolster it without compromising your theme.
I hope that helps.