Path of Exile is a deep game with many layers of complexity - as is natural for a long running free-to-play game. Warframe also has many systems layered upon one another competing for attention.
Skill Tree
The Path of Exile skill tree is a terrifying beast for new players - it isn’t after screwing up your first build and finding a few better examples that you finally understand what you are doing.
While I think it is part of their philosophy that it remains a large tangled web of both useful as well as less valuable nodes, the fact that it is difficult to weigh passive trees in-game is quite annoying. (We now have third party tools that attempt to help with this - Path of Building is legendary in the community for being a helpful build planning tool.)
There are probably a couple of avenues for making this more palatable. One options is that instead of having more nodes, perhaps nodes should be consolidated - costing more points, but having a larger total impact. This wouldn’t necessarily reduce the complexity or the difficulty of planning out a tree, but it would probably make it more obvious to a player which nodes to aim for. There isn’t really as much subtlety to skill point assignment as the tree would otherwise suggest - it’s really mostly picking out as many of the desired larger groups of nodes, and then picking up as many sockets in the tree as possible.
The other is probably having an in-game guide - this wouldn’t simplify the tree overall, but it would definitely be a huge quality-of-life improvement since players no longer need to constantly leave the game in order to refer to their planned build. I don’t think this would be a good use of developer time, however, as I believe most of their most devoted players would have very little issue memorizing massive amounts of the tree.
Combining Currency
Path of Exile has a lot of types of currency. I think there is room for consolidation of some of these types of currency without causing too much trouble in the economy while reducing the number of currency drops and inventory we need to manage.
Blacksmith’s Whetstone + Armourer’s Scrap
This is fairly straightforward - I’m not sure why these two items are separated other than modifying how we acquire them from recipes - they are pretty much used for the same purpose (upgrading quality on armour and weapons) and drop fairly often in reasonable quantities.
Remove Scroll Fragments and Scroll of Wisdom
Scrolls of Wisdom forms a fairly important part of the early game - during this time you are mostly in a “Robinson Crusoe” or SSF economy, where you have to be self sufficient. This quickly just becomes unnecessary inventory management kludge as you get through the first two acts of the game and becomes quickly irrelevant busy work (except for Strongboxes.)
Scrolls of Wisdom make up a fair amount of the drops, and if we just replaced this with a way to identify rares and uniques in town and had a timer a la Diablo III’s legendary timer for Strongboxes, I think we could do away with this currency entirely.
As for replacing its role in early game, I think simply replacing it with Transmutation Shards or equivalent and adding a little bit of back-end complexity for vendors being able to give you change for full Orbs of Transmutation would be sufficient.
Remove Portal Scroll
Speaking of another item that drops often, the Portal Scroll is another prime candidate. We use it everywhere, the restriction on quantity is pretty much non-existent after the first act of the game. We could just remove this and add a portal button. This invalidates the Portal gem, but really I don’t think anyone will miss it. (And I’m sure we can think of other ways to acquire Vaal Breach.)
Orb of Transmutation + Orb of Alteration and Orb of Alchemy + Chaos Orb
I may be missing a back-end reason, some odd crafting trick or perhaps a very good economy reason of Orbs of Scouring, but these currencies do very similar things. Transmutations make a random Magic item, and Alterations just reroll the Magic item. Alchemies make a random Rare item and Chaos just rerolls the item.
We could just combine both and adjust the drop rates and currency sinks accordingly. The only flaw I could see with this is that this may affect the trading economy - Chaos Orbs are currently the currency of choice but I think a little inflation for reducing the amount of drops and other things you have to deal with is reasonable.
Orb of Scouring -> Crafting Table
Scouring items to turn them into normal (or remove prefixes and suffixes) is a fairly common crafting tactic - this could very easily just be built into the crafting table and cost different currency (like a Chaos Orb.)
This suggestion falls over where you would want to scour items while in a Map. For example, Orb of Scouring + Orb of Chance on a specific base or bases to get a specific unique while under the influence of a certain League. The next example is Strongboxes - you often scour it to save Engineer Orbs.
This is probably sufficiently important to maintain its existence. (I still wouldn’t mind seeing a reset to Normal Item option for crafting in the Crafting Table for us more casual crafters.)
Blessed Orb
I see Blessed Orb as a peculiar beast - it seems to have a very singular purpose, that is to be a Divine Orb with a more limited scope. Given that most passives rarely have a massive roll range and the power of this currency is extremely limited in my opinion, I think that it makes sense to remove this as a currency and move it to the crafting table (and cost an appropriate number of Chaos Orbs instead.)
Maps
However, I hope that in future they prioritize simplicity and fun. It would be great if they removed the key dangerous mods from the pool (reflect, no regeneration, no life leech) and then added an option to just have the map device automatically consume the required currency to craft the map for those of us who just want to run through maps mindlessly.
Currency Auction House
I think another thing that would be nice is a currency auction house. We already have currency trading bots, and these make trading for currency so much better. It would be great if every player could participate - while this would definitely create a slight drop in the value of rare currency (and probably a massive drop in the value of very common currency) it would be a massive quality-of-life improvement for all involved.
A big concern here is that people may choose to play the auction house and constantly be trying to find arbitrage opportunities - but people are already doing this and this is already a valid way to play. This would just even the playing ground between bots and humans.