EDIT: Link to the spreadsheet mentioned later in this thread: https://spreadsheets.google.com/ccc?key=0ArE1chsgHXQodDd2ckdjLVY3Ujlad2tZWUpteDNtcXc&hl=en&authkey=CIrIhMwE 
The purpose of this thread is to discuss problems with using various gear shifters with the current MAME build and how a future build might best (and most simply) address these issues. This thread is not about using old builds or workarounds just to get the game working on your cab. This thread is also not to ---smurfette--- about MAME or the MAMEDevs.
What I would like to do is collect ALL the issues related to shifters and come up with ideas for some type of input system that addresses them all without having to hack all the different drivers in a bunch of different ways.
I'm not talking about just adding back support for old hi/lo shifters.
I'm talking about being able to play any driving game with any physical shifter setup and have it work correctly without doing much configuring.
I can't write code.

(odd that a thread about coding an input system should be started by someone with no hope of doing it

)
I have some ideas I'll put out there, more information will come out of the discussions, & eventually maybe we'll end up with some coherent idea that's specific enough that it can act as a roadmap for someone to write the code.
Here are Derrick Renaud's quick thoughts on how a universal gear shift port might work:
http://www.mameworld.info/ubbthreads/showthreaded.php?Cat=&Board=news&Number=232699&Forum=news&Words=IPT_GEARSHIFT&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=231686&Search=true#Post232699I'm an end user, so I'm starting from that perspective.
Here are my thoughts on how it might work from the UI
Starting out with an example a little more complicated than the Pole Position shifter, take Cruis'n USA
Input(this game) , we already have
1st Gear
2nd Gear
3rd Gear
4th Gear
So basically, you need a 4 speed shifter or 4 buttons to shift properly.
Now add two more options:
Gear Up
Gear Down
These would be mapped just like any other button and would work simultaneously with the 1st Gear, 2nd Gear, etc.
Kind of like how both an actual Analogue input, Analogue Inc and Analogue Dec all work simultaneously.
I realize that in the Analogue Inc example, those are two different types of input, but both options are there and they can both be mapped and used.
This would provide a good experience to those with sequential & paddle shifters,
which is probably going to cover the bulk of users.
But what about the people who like their toggle button in the current build?
Add just one more:
Cycle Gears
This button will bump up to the next gear until it reaches the top one, then it will reverse order or cycle around.
Again, it will be mapped the same as any other input and will work simultaneously with all other inputs.
I think this makes the latching (or hold gear) unnecessary, but I could be wrong.
There may also need to be a default gear for some games (not sure which ones had a functioning neutral).
This would restore functionality to Hi/Lo shifters where only the Hi position has a switch.
For those, you'd only need to map Hi gear.
Not sure how the Hard Drivin' analogue shifter fits in there, but ideally you'd select the input and move your shifter into the position for that input, same as mapping any other control.
My $.02 to get the ball rolling.
Opinions and good information wanted, ---smurfette--- ing not.