Eh, perhaps, but until powerleveling becomes fixed, this is pretty much a moot point, because one could probably spritbond their gear at around the same rate a gatherer could find +3 materials that could be used towards making HQ gear. Materia and HQ materials both require luck, both in terms of acquiring the ones you want and in terms of successfully implementing them into gear (the chances of getting multi-melded gear vs. the chances of getting HQ gear from HQ materials, THEN the chance of doing BOTH). Besides the customization involved with materia-melding, they both really boil down to stat-stacking, and with that in mind, I don't see why both materia and HQ materials can't drop.
Also, people can still spiritbond their gear into materia the old-fashioned way; thing is, depending on what gear they have, they may be limited in what materia they can obtain. I was wanting Touch of Rage IV materia for the longest time so I could tank easier, but it took me forever to figure out that you could only get them from belts (which I never converted a lot of), bracelets (never used them), and GLA and MRD weapons (I wasn't going to convert my best weapons). Besides, a lot of materia still sells for dirt-cheap on the markets anyways, unless it's the really rare and sought-after kinds, like Savage Might and Heavens' Fist, etc.
My suggestion is that, if SE wants to implement NEW kinds of materia (which I'm pretty sure they've already said they do), one way they could do it is by making it drop from chests, rather than people having to continue figuring out which gear turns into which materia. And it doesn't necessarily have to be BETTER materia; it could be stuff we don't have yet, like Block Rate, a combination of STR and INT, etc.