I think the loot cap is the most common cause of grumbling among the players i interact with and i think its an easy thing to adjust. But i regard that as a "rich mans problem" because it only affects those who are 1-enjoying the builder base and its unique features and 2-engaging in a lot of player versus player battles presumably because they like that format therefore painting the update as a success regardless. If either of those things were lacking they wouldnt be spending time on their builder base or hitting the loot cap or wouldnt care so much.
My perspective is that the more important variable for the long term success of the update is how time and energies spent in the dark village affects the main village and at the moment thats unclear to me. Given the dark village has different troops and defenses than the existing village with a different battle system i view it as really a different game, which some are bound to like better than the current game and some less. I find those who also play clash royale like their builder base a lot and those who tried clash royale when it came out and didnt enjoy it and stopped playing are more likely to view the builder base as a chore they would prefer to just skip (although even the most negative of the grouches i know still wants his gem mine). If you look at it as a game within a game your first reaction might be that any additional option for entertainment is a good thing. But the one feature that i see as becoming a bigger focus in the ensuing days will be the "gear up" feature. Because if progress in the dark village becomes a material factor in the defensive strength of ones main village and drives success from either a raiding or a clan war perspective that will turn this into a very polarizing event. If Supercell leaves the dark village without much impact on the main village those who do enjoy the new format and items will spend a lot of time there, while those who like the existing game better will probably carry on as they have in the past. That would be a win from my perspective. However if the gear up affects enough defenses and proves as material a change as adding an inferno tower or an eagle then those who like the game as it is will be forced to begrudgingly allocate time to the development of their builder base. As a Clan Leader that is where my attention is focused. Listening to my members grumble about the loot cap or the amount of draws they get or the fact there is only one builder is a minor nuisance that i know wont change their enjoyment of the game. But when i see the despondent tone of one or two of my best clan warriors who tried it out and really dont want to spend much time on the other side of the ocean but worry they might have to in order to remain competitive- that gets my attention.
I perceive Supercell has been careful with the impact and extent of clan perks due to clans earning XP only from clan wars, which presents a problem for those players who dont enjoy them. My feedback would be to keep the gear up or any other feature which makes playing the builder base game a "must" to a minimum so that this update will be a really fun added feature to some, and at worst a neutral to others.

