The coasters that were, gone for good?

First up is B&M's Dive Machine, the only two examples being Oblivion & G5, mirroring each other. How about one totally above ground with a 200+ft truly vertical drop? Add a giant vertical loop & other possible inversions. You want capacity? Have 16 rows of 8 across for 128 riders per train. :) I can see that now, Medusa on steriods.

Say, whatever happened to Arrow's 64 seat Supertrain?

Intamin Reverse Freefall (S:TE & T.o.T), surely the technology would be smoothed out & cheaper by now. Go full circuit & 300+ TA2K style hills would be the bomb. Use or forget the single cars & design longer, articulated trains, 4 or 6 across. Then again KBF's new ride could be this.

B&M Stand-Ups. Ok, more sucessful than the above. Just what is the story for their decline? I know the park decides on what ride they want, could it be they thought standing in line for hours only to ride in the same position was unforgiving on their guests? I had a stupid idea that they replace queue lines with airport travelators/conveyor belts with 500+ seats fixed onto them & guests just sit & chill out 'till their turn to ride. Btw, I'm waiting for RRV to lose it's crown to a bigger & 7+inversion Stand-Up.

Any other coaster types I forgot about?

Dont forget about Flashback, the Intamin space Diver.