That more stuff gives out myth doesn't really speed up the grind, it just makes it a little less tedious. Though that would depend on the drop rates. If it's much worse than Bray, then they'll be useless for grinding.
Have we heard anything about them increasing myth drop rate in 2.3? Because I know it was said it would happen in 2.28 and the increase there was negligible. Like 100 for low level roulette vs 70 before. Not a huge change.
I just spent all my myth on my second book, I'll probably be getting the 1500 for my next book right around the time for the patch. I should probably hold on buying another till then.
Changing drop rates during major patches is fairly common, and they stated in the past that they'd be controlling and reducing the grind for things like Books, Alexandrite, etc, by modifying the Myth drop rate as necessary.
It wouldn't require a huge change in drop rates, to greatly affect things, either. For example, if lvl50 dungeons like Brayflox, HMHM, etc, had their Myth drop rates increased from 50 to 70, you'd go from needing 16 Runs per Alexandrite, to 12.
If you were getting every Alexandrite that way, (nobody is,) it'd be the difference between 1200 Brayflox Myth runs, and 900. That's with a fairly modest increase to the Myth drop rate, and we very well could get a higher drop rate then that.
As for the 2.28 patch, only CT saw a major increase in its Myth drop, where-as the rest of the increase came from improvements to the daily roulette. I expect those Roulette bonuses to stay the same, but for the Base Myth drop rates to increase slightly.
Plus, again, you'll get Myth for doing Hunts and PVP, so if you really don't want to Grind, you can play normally and still get the Myth you need eventually.