Conservatives are generally older people, and younger people tend to be more liberal. Old people eventually die, so I think you will see a bit of a shift as the years go by.
Also, as the population gets more diverse, you would think that the minority population (which tends to vote more liberal) would start to provide that shift you're talking about. The problem with that thinking is that the more minorities there are, the more angry white guys who hate them there will be, and they'll be even MORE motivated to get out there and vote to "protect white America" or whatever (and now, having an unabashed racist/racist-enabler in the White House has normalized racism to an extent, so they're not even ashamed of their biases anymore, or making any effort to hide them). So I don't know that an increase in the minority population will necessary lead to increased voting for liberal issues.
I've found that the only way to keep right-wing-oriented people from voting for the R after a candidate's name is for them to finally wake up and realize that right-wing policies are hurting THEM personally. Only then will they be motivated to NOT wave pom-poms at "their team." It happened in 2008; it can happen again. I just think the Trump policies haven't filtered down enough yet for them to really realize how badly they're being screwed PERSONALLY yet. But I do believe it will happen. Just wait until all the people who whined about Obamacare raising their premiums get their statements from their insurance companies after Trumpcare (or as I think it should be deemed, either the FUCA or the RIPCA) takes effect.