I agree with most of what hes saying, but the keyword most is a clue into the epic breakdown I'm going to make out of his suggestion.
But what about ganking, warding and backdooring?
I'm not sure about you, but the more popular maps in 2v2/3v3 that I'm accustomed to playing: Prison, Exile, Cataract, etc.) are very easily back-doored. The portals are usually the farthest away from the citadel in corners, and will always have the fewest towers guarding them. Take out 4 towers and you can essentially backdoor and completely turn around a game. Same with fortresses: They're placed all-over and can easily be destroyed mid-game with an incomprehensible switch.
Some people proposed to make the vision radius smaller. In my opinion this is a bad move
So wait. You want the map bigger, more unpredictable and chaotic, yet you want to spare the smaller vision radius for claustrophobia? I hope you don't have anything against epilepsy.
/contradiction
Speed of heroes should also be higher, so that they wouldn't have to spend a whole day traveling to other side of the maps.
I hope you're suggesting that maps are exponentially larger in proportion to the speed of demigods, otherwise this is just a suggestion out of Texas.
This also makes the game faster & more chaotic, which IMHO is good for the overall gameplay.
While I'm not against this general statement, it's a complete contradiction. You want the maps bigger, yet you want them to be chaotic. You want the lanes to be bigger for more room, yet you want faster gameplay.

Let the maps have 2/3 (3 preferably) main lanes, and about 2/3 additional ones, that would allow heroes to implement some sophisticated tactics (flanking, ganking etc.).
This varies by map. First of all, you're mentioning 4-6 lanes for "maps," when the amount of lanes for each map varies greatly depending on it's recommended player size. The 5v5 maps will have up to four lanes, and two additional lanes, all containing vital flags including two portals of the four main lanes (5v5). You should probably list out each map and what it needs if you want this suggestion to be taken seriously, a lot of maps are slightly different, and have different elements to each. You're partially right, but way too vague, although I know what maps you're probably referring to and I can very easily agree if I'm assuming correctly...
Decrease the relative number of towers/defenses in the game - ie. the same number of towers, but bigger map. This way there will be more free space, where heroes could roam free, hence, DG would be more of an open game - not just fight between entrenched sides.
/thread
The more flags, the better the game

. Don't put too many on one map - just more diversification and everything will be just fine.
I dont think there needs to be any more flags. Most maps contain more flags than teammates to watch and control. Some flags are not nearly as useful as others. (Portal, HP, +damage vs. Mana, Cooldowns, Artifact&Gold, give or take an opinion or two.)
Make the terrain more interesting. Why we have to walk a flat floor - almost - all the times? Add some rocks, trees rivers etc. Of course don't make them too flashy, so that they will eat computer power even more - just let them look OK.
QFT
I completely agree. The maps are literally nothing but brick roads, towers, and a neat looking background. The game could take up way less CPU usage with better scenery over such high-res backgrounds.