I'd like to be able to choose to play matchmaking games without expansions, or select which expansions I'd like included, as a subscribed/paying member.
As far as I can tell, there's no way to change this option when I have a subscription, and matchmaking games are no longer fun when they're full of completely random cards - they often drag on for far longer than they should due to no card synergy and can be incredibly random/more luck-driven than skill-driven, etc. This is okay when I'm playing unranked games with friends, but when I'm playing ranked with strangers it doesn't give me what I want from the game, and I don't believe this kind of kingdom accurately reflects skill.
As a result of this experience, I have gone from playing every day before I bought a subscription, to having barely played at all in the weeks since I paid for a subscription. I regret this purchase deeply and would not have made it (at least on my main account) if it had been anywhere obvious that I would no longer be able to opt out of expansions for matchmaking.