What would the Thesis be? Obviously, the goal of any thesis, especially in Engineering, should be to advance scientific theory in some way. I just can't see what you would do that would be phd worthy unless you develop a new coil or something.

Now a psychology dissertation on why pinheads don't get laid as much as regular folk....

How about simplification of some typically complex and costly parts like drop targets banks?

Here’s one I found:

https://etd.ohiolink.edu/rws_etd/document/get/bgsu1120167127/inline

For M.E. maybe consider something like vibration modeling and reduction in a pinball machine or some kind of novel approach to fault reduction during manufacturing.

I thought of a perfect topic for this in the shower this morning:

You could investigate the problem of how to produce "floating" components which can be positioned on top of the LCD screen for the Multimorphic P3 pinball platform.

In case you don't know the P3 is a multi-game physical pinball platform. The top third of the playfield is can be swapped out to allow for many games in the same cabinet. The playfield surface of the lower two thirds is an LCD screen which provides dynamic and interactive artwork. Multimorphic has already developed floating slingshots and flippers which are positioned above the lower third of the playfield but there are also plans to produce other floating components for the middle third of the playfield such as pop-bumpers and saucers, etc., which will allow for more varied playfield layouts. You can probably get a better idea of what I'm talking about from this video:

In the video, you can see pop-bumpers in the middle third of the playfield but this is a concept illustration only, they haven't been developed yet. Also check out the Multimorphic website: https://www.multimorphic.com/

The creator of the Multimorphic P3, Gerry Stellenberg, is an engineer and a member on here and I'm sure he and the other members of the team would give you a lot of assistance if you decided to pursue this topic.

just spitballing -

reducing bill of materials/labor costs for under play field. Things like wireless power/control for coils/leds/switches etc.

Virtual pinball still suffers from poor physics. Work on what additional improvements can be made to produce lifelike real ball movement

How about the adoption of agile development methods in the mechanical and systems engineering space. There appears to be very little academic research in applying software design patterns to hardware and mechanical domains.

the application of a transparent LCD screen to simulate physics in a way impossible or impractical in the real world. e.g. shoot the ball into an area which locks it, but a virtual ball appears seamlessly on the screen area - where you can see the actual physical playfield underneath still - major crazy physics apply, (say, flippers that rotate around a virtual cam to hit a virtual ball, or a ball that only moves straight up and down and a second ball that only moves horizontally, and you use the flipper buttons to align them for some mode award). then when you "drain", the ball is released from the lock and real pinball continues

I was going to suggest a wireless switch system but I guess that’s more EE than ME, good luck with your thesis

Agile is a big space with a lot of big ideas. Check out a Joe Justice video on Youtube. He is applying agile to the hardware space.