My mates and I were throwing about some suggestions so I thought I'd bring them up here:
1) Allow parties to be made so you can play with your mates on the same team; but not above 4 players, not allowing for clans to just destroy casual people with 8 players - which leads onto my next suggestion.
2) Say clans do wanna practice with their whole team, create a separate lobby and server for anyone who has a party over 4 players, specifically to allow teams to practice with one another.
3) Most times you're waiting 20 minutes+ for a game, and you'll get to 15/16 and someone doesn't accept, most likely cause they forgot. Maybe create a warm-up server so players who're waiting for a match can practice or something, then somehow have an in-game notification pop up saying that your game is ready, I dunno.
4) I don't like draws, can we include a tiebreaker map? (Not Winterburg, as OGL pointed out recently after a game, it's surprisingly not great - sorry).
5) Increase the accept timer to maybe 8-10 seconds, I've sometimes missed it cause I couldn't alt-tab quick enough.
6) Create some sort of balance in the lobby - with the pre-chosen classes, I've been in teams where there's 6 cav and 2 archers - so you end up fighting for the classes in-game and end up playing a class you don't want to.
7) On open maps, perhaps increase the cav limit? It really restricts your tactics and setups always being 4-2-2 - it gets boring really quickly, having that ability for one more cav would make things interesting; if the strat gets annoying, people aren't afraid to tell you to change class.
8 ) Have a separate lobby for a 5v5 option, so you can get quicker games and less waiting time for people who want a quick game.
That's all I can think of for now - also apologies if it's not in the right place, I was lazy.
EDIT: Credits to Shingen for most of these