Quoted from flecom:

you ever owned a machine with eddy sensors? ToM? CV? etc? they are a pain and take up a lot of space under the playfield for the detector board and then the amplifier board

Quoted from dagamedoc:

I think that right there would kill all possibility for it being implemented...they cant even cope with the software they have NOW.
Still, it's a GREAT IDEA. Possibilities for some self-contained mods are rolling through my mind...lol.

Quoted from Wolfmarsh:

On a recent pinball trip, pinsider Kniessl gave me the idea to do more with the backbox. With just the LCD and no control boards in the one for Spaceballs I had a lot of room left over.
We came up with two major ideas during the discussion that will make it to the actual game.
The first is to have a thin exhaust channel on the sides of the backbox aimed at the player that are fed by a squirrel cage fan. They will become active when megamaid switches from suck to blow.
The second idea was to have the bust of megamaid rise from inside the top of the backbox when her mode starts. It would normally be hidden inside the backbox. This is just a simple belt driven lift or a scissor lift.
Both of these features will be active during certain attract modes too.
tl;dr - I think backboxes still have a purpose.

Quoted from megadeth2600:

While I am not an expert (i.e. I could be missing something), I think you can make these switches reliable by processing them digitally.
On the games you mentioned, they were using an analog solution. They look for a change in reference signal amplitude to detect the presence of a ball. The problem you run into here is that the sense amplifier drifts over time due to various factors (temperature, changes in semiconductor properties, etc) ... that's why you need to tweak that pot on occasion.
I believe there is a really good product out there for these games that can self adjust so that you don't have to mess with that pot every now and then.
Doing the sensing digitally can make the circuit a lot more reliable. The tradeoff is that you need more processing horsepower ... especially if you want to sense multiple switches! There's also a change in frequency when a ball is present. It's more difficult to sense this using an analog circuit, but a breeze to sense this digitally if you have more processing power. Since the processor in a modern pin is a lot more powerful, you can do a lot more signal processing to detect frequency changes to the reference signal.
One final note ... "analog" does NOT NOT NOT imply "bad" ... marketing people hate the word analog since it implies old/unreliable ... bad digital solutions can be a bigger nightmare to maintain . They used an analog solution since the older 6809 probably couldn't do everything that it needed to do to detect frequency shifts while driving the entire game. You need to sample the signals rather frequently to resolve the state of the Eddy sensor. That chews up cycles on the processor.