-Choice to randomize weapon variants, like you can with highlights, skins and victory poses.
-Option to randomize out of 3 loadouts you have set.
-Same as above but for mythic skins choices, like colours etc.
-Being able to ping through windows of enemies (or constructs such as traps/turrets.) Not currently possible, since it will just ping wall "over here". Maybe there is reason, it is not possible but would be good for those, who do not communicate in voice or text. Punishes opponents, who push too far into spawn and can warn teammates.
-Ability to modify hero grid in some way. This is quite reaching and i doubt, it will ever be possible. Would be cool to have it, like dota has.
-Being able to modify UI or interface. Such as centering skills on middle of screen or to sides of crosshair or wherever you wish.
-Ability to show preferred heroes in pick screen/banning phase. Yes, you can do this but only to 1 hero currently. If they made this better, you could even have game itself show statistics/hero history for your own teammates over hero pick grid.
-Show hero chosen in queue "screen", where you can normally put specific hero (or one you played before) for test of the people in your own team. Currently, it only shows yourself and nobody else. It could be simple small icon next to them even, if actual hero animation next to your hero is not possible.
-6v6 stadium, though i really don't expect this to be ever the case. Would be too hard to balance it for 2 tanks. Maybe make it possible as quick play option? This does however fragment players even further, which would push queue times further up. Stadium already has issues with that for support roles.
-Ability to queue for multiple modes, arcade, stadium, 6v6, 5v5 etc. Once again, i don't expect this to go through for reasons above of fragmenting population and driving queue timers up further.
-Better practice range. This should be improved so much, since one in workshop is way better. Such as ultimate pack being on slight timer. It should be instant. Of course, you can ignore it and use one for workshop but for some people, i don't think they find it or even know about it.
-Some kind of clan system. I know, this is not exactly big thing and i doubt, it would change much for me either, since i am more of solo player but it can't hurt either.
-This is more of inspiration from dota but maybe what dota calls "weekend battle cup" tournaments, where people sign for them and winner gets some currency to use. This is fully automatic in dota. Maybe give winners some incentive to win, such as minor rewards.
-More slots for items in stadium for saved builds, so that you don't need to leave options or choices out of it.
-Ability to "quick buy" items on next round of stadium or whenever next round starts. You could "mark" items, that game automatically buys next round or even have option to "quick sell". Time is already limited, so this would help somewhat, in case you have extra time previous round to think. Instead of just waiting for round to start.
-Tab in stadium, that shows certain items, that team has. Such as healing reduction/movement reduction etc. This could be limited, such as dota has, that shows "team" items. It could also show, which items someone in team is about to buy. Yes, you can check this in tab currently but you have to hover mouse (if you don't remember icon) or just remember icon from memory. Time is limited, so this could again make checking things faster. Marking items/powers you are about to get too.
Anyway, just a couple ones, i came up with. Hopefully at least some minor ones could be considered or be added on later date. Feel free to discuss or even add your own ones