We all know that, on top of the fewer population, a lot of people have started playing DTV instead of battle/siege, just for the rewards, thus involuntarily contributing to battle/siege's "death".
The typical solution in cRPG, I guess, would be to nerf DTV rewards back, leaving them inferior to the other game-modes in average.
My suggestion is the opposite:
increase the rewards of every other game-mode, making DTV inferior again - not a grind game-mode but the newbies and noobs game-mode it always was.
You may think this solution would be too much, making levelling up too easy, or "destroying" the concept of cRPG, but, at this stage, I think that boosting xp and gold gain would actually attract more players, both old and new. Given the current population, I think that faster levelling up and heirloom acquisition would be motivating. I think the concept of cRPG is not just levels or the grind, but the best modification of Warband, with its unique different game mechanics and features, and the optimization with WSE2, and, by shortening the grind, the mod would be more dynamic.
By
tripling the rewards (both xp and gold) of Battle and Siege, these game-modes would yield more rewards than DTV again, and, at the same time, still be more fun (to a lot of people), and, if you think about it, e.g. a Battle round with x5 that ends in 4 minutes would give you 3750 gold (DTV max reward is 3000 gold), and, if the round lasted longer, even more gold. The xp gain would also be higher than DTV's maximum.
If you think it's too much of an increase, you could tone it all down, including DTV, but I suggest both xp and gold rewards stay higher than the old.
Best game mechanics + smaller grind = more dynamism + more players.