Seeing as the system is able to communicate to the database that you won the last round and that you should get x2 xp for the next one, I assume a win/loss ratio is perfectly doable.
And on that note I highly support it being displayed on the website, although I support any ideas of presenting us with statistics, statistics are fun. Regardless of that I feel that win/loss ratio is a very interesting statistic as it shows your success at achieving what is for me the ultimate goal of any round you play, winning said round. Score and kills still miss numerous actions that can be very important for winning. To name a selfish one, the fear factor of my pike in an engagement heavily influences my side's chances of winning that engagement regardless of whether I deal damage.
I think it would be a good idea to track this statistic, not only just for show but also to base team balance on if it isn't used already. It simply takes everything into account, most importantly it perfectly balances for banner stacks. In any case this could be an idea for the new game, win/loss ratio becomes quite a reliable measure for your worth as a player in an objective based game mode if it is based on enough rounds I'd say.
Win/loss ratio would probably be more volatile than k/d ratio, but i supose that the more the merrier.
I'd think win/loss ratio would be very consistent and I'd presume that the best player in the best banner stack has a win/loss of like 1.4 and the worst random of like 0.8, the differences could be even smaller.