As said above, it increases the chances of the boosted units in Gacha.
The problem is, since Nutaku doesn't do patch notes, we don't know are we getting this or not.
Also, to be noted is that this doesn't really increase your chances on a grand scale. When the game launched, let's say if only Sol was boosted, your chances to get Sol was 5/12, if I understand how this thing works. That's ~42% when you land on a SSR Hime. Now, your chances to get a boosted Hime is 5/34 (~15%) and if we get this change it'll be 15/44 (~34%), so it'll still be worse than what it was at the start of the game.
A very welcome change, especially if you're hunting for new SRs. It's great for SSRs as well, sure, but SSRs will still be far too expensive to buy for most.