We started seeing a noticeable drop off in revenue in the early 2000s - the innovation went, the jackpots went up and the % went down. Also, on a human level, a lot of good designers either left or moved to the USA to work on casino games (Barcrest USA). The UK really suffered from that, I think.
Although those designers didn't have a lot of success in the USA
The only people that really want higher jackpots are the pub co's and arcades - the manufacturers (and certainly the game producers, like me and Ed) DON'T want higher jackpots. The jackpot to stake ratio is really important - the best days were the 25p, £10 jackpot days - a 40 to 1 ratio seemed good. 30p / £15 was ok and so was 50p / £25 as they both had a 50 to 1 ratio, but once the stake went past 50p, and the jackpot past £25 it got silly. Players used to love pushing for Jackpots, knowing it wouldn't cost them the earth - but nowadays, that just simply isn't possible.
I doubt a RollerCoaster ( , £10 version) would take any money if you put it in a pub now because people are so used to the DOND feature and seeing the big £100 there somewhere, that i just don't know if you can go backwards successfully... although, i do have an idea of how to do it