What's the lowest value you could possibly have gotten with the compromise?
Let's assume the absolute worst case scenario: you bought every expansion, all at once, a day before they unveiled the subscription model on MF's client. You hadn't heard this announcement in like February or whatever, and that's reasonable, it isn't easy to find if you aren't into Dominion a lot (though I mean, dropping $110 on a game you don't Google quickly first, strange). Let's then say, you are taking the free year online, because offline forever is boundless value and we can't quantify that.
So on, June 30th? You pay $110, and you get 18 months of Dominion Online. This is $6.11 a month. It's suspected, but not confirmed, that $3 a month is the buy everything subscription price. Man if that goes up to $5 a month won't you have some serious egg on your face, quibbling over $1.11 a month. But anyway.
A more realistic case: You payed $100 in February, right before the announcement, then didn't buy Adventures, because what's the point or something. That's $100 for 22 months, $4.50 a month. Still like 50% more than the pure value if Shuffle IT existed the day of the announcement and charged the price they wanted immediately, but whatever.
Anyhow, my point here is, you've got reason to be upset, sunk costs and all that, but dude, it isn't that much money, and if you hate them so much for doing this, you can go ahead and only play the game for another 16 months for "free" and then not continue. Wow, it's really hard to be mad at some people while playing a game they didn't have a legal obligation to give you for 16 months but chose to anyway to make it suck just a little bit less.
But really dude, is like, maybe $40 ish of value lost over the course of a year and a half really anything to write home about? Like I subscribe to two different music streaming services for $10/month because I can't decide which one I like better. Any lost value for me I'm not going to notice. I know some people have less financial stability than others, which would be a very good point if this money wasn't already spent and gone.
If January 2018 comes, and you're still upset about this, and you don't think the new client is enough of an improvement for it to be worth it, then cancel your account. What's the big deal?