Quoted from mbaumle:

Any cell phone app integration. Connect the pinball machines to wifi or bluetooth and create an interface so that people can interact with the game from their phone. Maybe an achievement system, or a way to "save" your progress on the game to encourage repeat plays. Heck, maybe even integrate apple pay or android pay so that coinage doesn't have to be an issue.
Also, connecting the pinball machines to wifi could give them the capability of automatically alerting the operator via automatically generated email or text message that certain functions of the game need servicing (broken switch(es), solenoids, bookkeeping alerts, etc). I'm really surprised that hasn't made it's way into the software and hardware yet.

Quoted from Plungemaster:

Open source code with supported mod tools.

Quoted from PanzerFreak:

Game companies selling titles on Steam allow many of their games, including those with copyrighted music such as Grand Theft Auto 5, to be openly modded and those mods shared with other users. To get around license holder concerns with modded code manufactures could implement a setting to only allow modded code to run while a game is in free play mode.

Quoted from VacFink:

I've considered this in a two (or more) game format I considered building called 'hot potato' the idea would be that completing shots would block shots of the other play or limit access to ramps or shots and upon completing the 'pass off' they would switch roles. Both playing at the same time, but with different goals.
However I thought a physical connection was problematic. Instead you could do it digitally via signal or wi-fi, or even over the internet, which would be interesting, with activation of a ball transfer via subway or even just normal eject from a captive location.
This would provide for some fun tactics. For example, the 'hot potato' holder is flipping to pass, their score decreases as long as they hold the 'active ball' and shoot a series of shots to transfer. On the defender side, they are shooting to activate blocks (resetting pop up targets with a combination of shots, keeping the 'pass hole' shot blocked, or even making point in other combos to offset or gain on the opposition.
I'm not yet to the point of making a first game but think it has potential for fun.

Quoted from Darcy:

The ability to enter your skill level, before staring a game. Give at least 3 options for players to choose from. Some choices could be Child, Novice, Average, and Skilled. The adjustments like Easy, Normal, and Hard could also be used.

Quoted from toyotaboy:

I think it needs to be better than choosing. I think a pinball should adapt according to how you're playing in realtime. If you start playing really good, maybe the outposts are movable by servo control.. Or the coils on the slings adjust power to aim the ball towards the outlanes, or maybe a reverse kicker is inactive inside a gobble hole until you start having a good ball. Not saying this would necessarily work for tournament play, but for location pinball this would keep long ball times down (but give novice players a fair chance). this is how slots work, it makes you win at first, but then starts changing odds so you lose. It's what encourages gambling more. Imagine the same kind of adjusting difficulty on a pinball?

Quoted from WH20_Buzz:

Decent quality Speakers would be a good start

Quoted from pinlink:

It would be cool if there was a mode (maybe that you tried to avoid), that released other balls onto the playfield that were not the standard steel ball, and were meant to make you lose your ball (the one that counts). They could be similar to the powerball in TZ so the machine knows when/if you lose your actual ball you are trying to keep alive. If you have played the PinOut app, this is where the idea came from. Here is a screenshot to better explain. Your ball is the black one, and these red balls are released making it difficult to keep your ball alive.

Quoted from gstellenberg:

LL-EE on the P3 has this. It's tied into the player profile features which also let you change the game settings per player. We excluded ball count from the save/restore to avoid weird situations with multi-player games.
Longer term, this will be a framework feature available to all games on the platform.
- Gerry
https://www.multimorphic.com

Quoted from yellowghost:

Maybe like a option where you can type your name if you wish and the game can speak it instead of "player one" or "two"
Idea 2 would be color changing GI strings with remote or app and the owner can change the color to which ever they choose..like pin-stadium.