Although I haven't been super impressed with his tennis game yet; Kyrgios has shown some very encouraging signs at a young age. At 19 he's made 2 slam quarters and on more than one occasion saved match points to come from 2 sets down to beat good players. You would expect to see something come out of that as it's so difficult to do, and it's not that he's been a workhorse in his teens like Nadal. He seems to be a naturally a good athlete.
I also remember being impressed at Wimbledon that he had the audacity to toy with Nadal; and I don't mean the famous shot between the legs, I mean serving into a place when it could win him the point while making Nadal look a bit silly, rather than going elsewhere out of respect; so there's a competitor there. The question with him is that he appears to be another temperamental aussie who may not have the love/dedication/discipline for the sport that you need to make it at the top and might stop progressing ala Tomic.
The other issue with Kyrgios is that by the time he'd be ready; the OG would be at the stage Federer is at now.
If we're talking about any of these guys getting to a stage where they lead the tour and take over to a comparable level as what we've seen with Djokovic, I'm not seeing any signs of that. There could be a period similar to the one between Sampras-Agassi and Federer-Nadal, where we see good players trading slams with the aging guard and the streaky players who can put a good run together now and again.
The way careers are lasting these days, even with Djokovic into his 30s, it could be similar to the WTA & Serena where the tour still has to hope she's having an off day. Hopefully it doesn't come to that.