Based on what SE said, I think you're right... the end game crafts will almost certainly not be guaranteed to HQ if you don't have the best gear with some melds. The question is, will they make the quality requirements high enough, or will someone who melded tier 8 into all the guaranteed slots and slapped on a bunch of tier 4 overmelds be able to 100% the crafts from zero quality. If someone with mediocre melds like that can still 100% crafts from zero using a fixed macro, I would say nothing has changed... hopefully this will not be the case. Just my opinion, but if someone has not bothered to do good melds, then they should be forced to use HQ mats in order to HQ the end game crafts consistently. Like, take your pick, spend the extra effort melding, or, spend the extra effort making some HQ mats.
The difference with melds is significant, for my characters, only one is max melded which at the time cost roughly 30 mil gil worth of materia (although I made most myself). The following are the differences in stats between a max melded crafter, one with tier 8 in guaranteed with tier 4 overmelds (which currently costs under 2 mil for the tier 8's and about 500k worth of tier 4), and one with no melds at all (craftsmanship/control/CP):
Max Melded: 2316/2332/541
T8 w/ T4 overmelds: 2183/2181/541 (see
https://ffxiv.ariyala.com/1B1MN)
No Melds: 2087/1942/449
I've heard many say that melding costs a lot, but 2.5 mil can be obtained in a single day by just about anyone. It would take about 8 hours of gathering, or 10 hours of doing FATEs / hunts, etc. Or you could obtain the materia yourself for free, for that amount of materia it should take someone all of 6 hours of combined gathering and crafting collectables for scrips to get materia. If a player cannot be bothered to spend several hours preparing their crafting classes for end game content, then I don't really know what to say, and I don't know why they bothered spending dozens or hundreds of hours leveling their crafts in the first place.