i can't help but suspect most players are just not interested in playing solo. it's easier to get a blitz or an antichess game than a regular solo game.
it's also not that hard to get a solo blitz or bullet game running, which i think is understandable, because solo games tend to take soo long (if played correctly...).
that said i would like to see many more solo games, because most ffa player whine about cooperation and teaming and essentially refuse to play ffa and play a solo style despite games being ffa.
my idea would be more like some matchmaking preference settings
[x] play solo games
[x] play anonymous games
and have these checked for everyone (or for some subset of players) by default, meaning that when they click play or play again, if there are solo or anonymous games waiting to fill up, they will sometimes be but in those games too. And be forced to go uncheck those settings if they don't like it. I'm not sure this won't upset people though or cause too much confusion, maybe Bab can say.

So I did a little experiment today. Over the past one and a half hours I set my game search filter to only solo, and also set the same settings for the watch panel. You know how many games/queues I saw during that time? 0. Yes, zero.
Which brings me to my next point. The leader board. Presently (6:44PM CET 19/07/2019), the #20 rated player is 1641. I don't have a screenshot of the ratings right before the update, so I will have to use the WC qualification as a reference point. The #20 rated player at that time was 1750. That's a 109 point drop.
Now, we could argue about the reasons why, but it's obvious Solo is dying (or is already dead), and this trend began following the update, which removed forced Solo for 1550+ players.
I've spoken about it with NeoSerbian yesterday, and have thought of 2 possible solutions:
1. Force Solo for high rated players again (same as pre-update).
2. Make Solo (rather than FFA) the default option when starting a game (at least for players >X rating or players who've played >Y games). I think this is a much better solution, as it would allow players who want to play FFA to still play FFA, but would, at the same time, create a lot more Solo games, since, probably, a lot of players just click play without delving into the details.