Take a look back at all the communist countries ever in existence. Every single one of them has been plagued by a mass killing of its own citizens. Since we have some precedence for how communist countries act all of the time, it would be foolish for us to think that they would do anything any differently this time.
Yes, I think that there will be modern mass killings revolving around Communist regimes, because that is already happening. North Korea is the ultimate Communist regime, and people die in that country at the hands of their government all the time. Where resources are scarce, the government picks scape goats so that people will blame each other and not the government.
There will not ever be modern mass killings revolving around Communist regimes. At least I would hope that this would not happen but anything is possible. It takes a leader to provoke this kind of action amongst its country. The leaders that we have now would not let this happen.
There will not be any more mass killing from Communist regimes because there are not any more legitimate Communist regimes. Although some countries still call themselves communist, they have almost completely abandoned all the ideals of true Marxism. The international community will not allow any more mass killings to take place.
I do not believe we will see any modern mass killings revolving around Communist regimes in the future, at least not the short term future. China, Cuba, Laos, North Korea, and Vietnam all claim this title. Of all of those, I would say the only possible one as of right now would be North Korea.