I think this is a good proposal, we need the game to be more fun, we need new game modes that people want to play.
As for the economic details, it should not be such a big problem if the DEC or the reward that will be delivered will be in "Guild Power", to my way of understanding things, this will not flood the market with thousands or millions of DEC, but it will be a door for the guilds to continue to grow.
Another thing if they don't want the DEC to get involved or something like that, the rewards could be special cosmetics for the players, in this case those who participate in the tournament, when I talk about cosmetics I mean :
- Skins
- Profile pictures
- Maybe Soulbound Titles that classify players by their performance in the guild war.
Be that as it may, you have to make the product have more ways to have fun, at least in my opinion, this would imply more hours of gameplay, more time invested in splinterlands, which could imply more investment in everything that is currently needed to play.