There's a few things that could help boost its popularity, if that's even an issue. Some of these suggestions may turn off current fans, but it doesn't have to be either/or. These things can happen without displacing the things we like about pinball currently.
1. Get it in places other than bars so that younger people will get interested. Host youth tournaments as well. Make it a social activity to get teens out of the house and interact with others. (I know mine needs to)
2. Themes that younger people will be interested in. I wouldn't go super young, but more of the 14-24 year old age group. This is always going to be challenging as what's popular is constantly changing.
3. More digital features in games. It occurs to me that Insider Connected is a huge step in this direction. It adds a lot of interest and replay value to be able to record your scores and play for achievements.
4. Official digital pinball tables to make home ownership more accessible. I would never say that digital=real pinball but it sure is an appealing thought to have a digital cabinet that can play all your favorite games for around $1000-$1500. I doubt this would ever displace physical games or even take a bite out of the market for them. I'll always prefer the physical game but not everyone can buy one.