Not sure if this topic is here for Faction Challenge change suggestions in general or just this one idea, but I trust a kind moderator will guide my post to the right place, if it's not meant to be here.
So while I think faction challenge is a solid idea, we've seen several complaints and unfortunate side effects because of how it was implemented on recent challenges. I collected a handful of problems and possible solutions to them. Some of them were already offered before by others and I meant no copyright infringement, so feel free come forward for bragging rights if you like.
Reward system
We've seen complaints from two sides in last two faction challenges. One side argued that winner faction supporters should get some form of reward so the event actually warrants as a faction challenge, other side argued that it's unfair if active supporters of losing faction is less rewarded than a winning faction supporter with only a couple of wins. I think truth lies in the middle and by applying a combination of solutions used in earlier challenges.
So I would keep the ladder from last challenge maybe with some tweaks on rewards and number of required wins (see section on grind). On the other hand I also think that winning faction supporters should be rewarded in some way, otherwise there's no stake in the faction war. I would require contributing a minimal amount wins to get this reward, not too high though that even a casual player would find it too difficult to achieve. This reward should be something only affects flavor like meteorite powder and/or a unique title. I've seen the outrage of people not wanting to be left out of unique rewards and I can feel their pain when it comes to borders and characters, but maybe will be more tolerant with titles as there are lot of those out there. Thing is I feel some trinkets should not be available for everyone in order to hold some actual significance.
Standing aka The progress bar
Some people complained about wanting to see a progress on current standings in the challenge, i.e. which side is ahead. It's true, not that inspiring to push for more wins if you have absolutely no idea what's the current standing, no reason to rout for your side, etc. Now I see the problem with this is dogpiling on one side or committing late in the challenge to the winning side.
I have two suggestions here:
1. Make the challenge two-phase. Say challenge is 10 days long, then you have the first 5 days to commit to the faction of your choice. Hell even make the choice mandatory first time you start Gwent after the challenge is started with a popup window. It would at least prevent players from getting rewards when they forgot to commit to a faction as it happened in last challenge to some people. During these first five days standings would hidden just like now. After that when when faction commitment is frozen, standings could be made public.
2. Against dogpiling I would make only best N player's result count for each faction. N could be fixed number like 1000 or 10.000, or alternatively could mean number of supporters of the less supported faction. This way one faction wouldn't have more wins simply because of more supporters. (Of course it's a limited effect, more supporters still mean better odds, as from a bigger pool you could get more good players, just like the national team of San Marino doesn't stand a chance against the national team of China in any sports.
)
The Grind
We've seen pretty much no other decks played than SK or ST during the challenge days as people desperately tried to get their 50 (40, 30, ...) wins to get the rewards. They even went so far as to grind the casual match scene with high powered netdecks, so I've heard. Now you know something's very twisted, when that happens. The Casual area is there for newcomers and casual players to get some sense of success and experienced players to run some weird niche decks that involves Ciri: Dash or Gaunter O'Dimm.
My suggestions: make the ladder less steep requiring less wins for full reward (or maybe apply diminishing returns like on daily rewards), and/or exclude casual games out of the challenge to keep casual area safe from abusers.