I am exited for the Mcgregor-Diaz II for a couple of reasons: first, it is an extremely ballsy move to get from featherweight to welterweight (although I believe Nate wasn't that much heavier in their bout), which kinda tells me Mcgregor is not only in for the money, he was having tremendous success beating featherweights who he could shrug off with his physicality and who couldn't handle his power; the moment he moved up he would be in a pool full of guys who are physically more stronger, hit harder and could absorb more power. Why would you stop doing the same old trick when you could cash in doing the same thing taking relatively little damage? He could do a Aldo rematch, he could do a Holloway rematch, he could do a Mendes rematch, he could fight Frankie. Non of them would be easy fights, but I would guess he got more of a chance beating 2 or 3 of them in a row than beating RDA or Diaz. This makes me feel he truly tries to build up a legacy that could be remembered.
Secondly, he finally seems to have found a true rival. Mcgregor-Aldo had a crazy hype-train going, but now he met someone how could beat him. Rivalries are are the highlights of legacies. And it might make him a better fighter since he got a chance to learn from a loss.
About grappling only events: nah...there is surging number of events for that niche already (EBI, Polaris, ADCC, Mundials, etc.), and it just doesn't excite most of the fans.
About striking only events: nah...same as above, but the fans do find striking exciting.
What made the UFC was, and is, the utter simplicity of it, minimal rules. That is made it the home and testing ground of all kinds of fighters. When I watch Glory, I get fed up with the restricting rules. Even more when I watch the Olympics and see TKD, judo and boxing which have become not much more than exploiting the meta of a game which has very little to do with a fight. Same with sport jiu-jitsu.
TLDR; Mcgregor-Diaz II got me going, UFC should stick with their format.