Strategically the best thing you can do career-wise is to write something with multiple chapters on a common theme but with each chapter understandable separately with a minimal introduction, get each chapter published as a separate conference paper, and then stick them all together into a thesis. Then you not only have a publication list all ready by the time you graduate, but you make it awkward for the examiners to find fault with your thesis given that it has already passed peer review. You'll probably have to pick the trendiest topic you can find even if your interests lie elsewhere, but you'll be in a better position to vary your research agenda when you're more established in your career. This advice is the opposite of what I was given, which is that a Ph.D. is a time to explore your own interests and then get serious later.