Without Elder Dragon, you can put in two extra units in there, which could be Gnar and Alistar for 2 Brawlers and 3 Elderwood. Which makes your frontline much tankier.
Gnar and Kennen are more flexible with items. They are better with Thief's Gloves (TG).
Easier to tag in Lux, since you have freed up two slots.
When we have Executioner Emblem for Draven, we could also tag in Soraka for more Executioner to buff Ezreal, Kennen and Draven altogether.
Disadvantage
Less threat to enemy backline, Elder Dragon's ult combined with Draven's ult could one-shot enemy backline.
Elder Dragon can active 3 Riftbeast for the Sentinel (Blue Buff). Without Elder Dragon, it becomes less optimal to play Sentinel as the main tank.
Elder Dragon could solo carry really hard when 2-starred and has great items. (such as Radiant items and Artifacts)
Opening
Prefer Elderwood + Inferno opening, this is the most smooth and strongest opening to pivot into Draven 95.
Later on transfer Varus items → Ezreal
Xayah items → Draven
And make Thief's Gloves if you can!
They will give great tempo. Later on put those Thief's Gloves on Gnar and Kennen.
Building Frontline
Itemize 4-costs tank first. Amumu does a great job before Taric and Maokai get upgraded to 2 stars. Sett and Sentinel are also accetpable if you didn't find Amumu, but they're not ideal.
If Taric and Maokai come around the same time, Taric is much better.
Maokai is only better if you find him a lot earlier than Taric.
From my experience, Gargoyle Stoneplate is not very ideal in this comp. Try building Evenshroud and Protector's Vow first.
The Importance of Ivern
Ivern gives a massive amount of shield! Especially if you give him multiple mana items, such as Double Spear of Shojin or Adaptive Helm.
If you have extra mana items, consider putting them all on Ivern to shield your frontline. This will buy Draven more time to deal damage.
How to pick Draven's Quest/Bounty
In general, the quests that only require Draven to deal a certain amount of damage are the best. They allow you to generate gold safely. The amount of gold in the quest can vary based on how much damage Draven needs to deal.
The ones that require Draven to get a certain amount of kills are much harder. Assists do not count as kills in this case. Draven has to actually last-hit the enemies, so you need good Draven items and can't have your other carries too strong. This makes the quest very tricky.
With Guinsoo's Rageblade, Draven normally casts 2-3 times per round.
The bounties that require Draven to cast his ult 5 or 8 times are also pretty good.
The 5 casts one gives two 4-cost champions, which is equal to 8 gold at least.
The 8 casts one gives 10 free rerolls, which is equal to 20 gold. This is much better. It could actually help you 2 star your 5-costs.
So basically, you get around 4-5 gold worth of resources per round.
Here is a simple sheet for the Draven Bounty (which we will update consistently as patch goes on)