I feel like luffy is overhyped. Why be hyped for a guy who is already hyped by the masses? And by the way, luffy might get a new fruit, the reason i believe this is because possibly, the D family has this weird trait of being capable of consuming multiple devil fruits. Or at least might be a part of it. A new devil fruit is not an impossibility but i don't think getting WB's fruit is the best idea, that'd be too uncreative for something like one piece's story. It would be better if he get's a hashirama-like power, something which allows him to summon some kind of weird creature from different worlds, his bodily boosting is too buffed already, it's too unlike luffy to be buffed this much, he wouldn't be an "underdog" if this continues, it'll entirely overturn one piece's story upside down. So a power which wouldnt affect his current body since he has more than enough buffs, that he looks totally uncool now, the post timeskip starting was too hype compared to these recent chapters.
Firstly, what evidence fuels your speculation that there's a correlation between Blackbeard having two fruits and being a D? Only one character in the series has ever had two DFs, and that one also happens to be an anomaly in terms of how he acts, compared to the rest of the D's.
Secondly, I don't think he needs a second DF, because frankly, it's more enjoyable to see him defy the odds with a fruit that does little more than make him stretchy.
But, assuming he had to inevitably have another, I do agree he doesn't need another physical buff. I think a Zoan is also out of the question, because that's also still kind of a physical thing. A Logia would be acceptable, but I'd prefer to see a tactical Paramecia in the vein of the Ope Ope. To be fair, I am admittedly a huge fan of Law, and I think that's the single greatest DF in the series, but for me, the less blatantly powerful the DF, the more enjoyable it is to watch. Ope, Gomu, Ito, Hana, even the Hito- I'd want a fruit like those, where the potential is limited only by creativity. I just can't think of one that would drive the series as much as the Gomu has.