In reply to waterfall:
Good job.
I'm in the same position as you (ish). Completed main Wainwrights (7 books) in 6 years in 2017, and was looking for other similar walks/projects (and still am, so appreciate everyone else's ideas!)
Have you thought of the Outlying Fells (the eighth book). They're quite fun, and a lot more remote. They took me 5 years. I did the lot in 10 years (ish) start to finish (June 2011 to July 2021).
Also, have you thought about submitting a report to the LDWA Hillwalkers register https://ldwa.org.uk/hillwalkers/hillwalkers.php
I started the Wainwrights to make myself go and explore hills/walks that I wouldn't otherwise go to, get me out of my (walking) comfort zone, I'm not really a list ticker (try very hard not to be!)
I read about the Ethels (Peak District) (map: http://pnfs.org.uk/ethels) which are quite fun (and an added attraction of the Ethels is that you can do quite a lot of them by train if you are inclined), and I'm nearly done. I was thinking I was ready to get back into the Lake District and may go round again perhaps via the Fellrangers list. But someone happened to give me a list of Lancashire trig points (https://goo.gl/maps/NY98oR8GiKzqG6sWA) which make great walks and go to some different and wonderful places: many are walkable, some are not even remotely interesting to walk (and maybe I should allow myself to cycle), some are a drive-by (literally!) in a car, and some do not have public access (there's even one Wainwright Outlying fell that is on private land and doesn't have public access). But it takes me to different places that I wouldn't otherwise have thought: who'd have thought that a trig point between Morecambe and Lancaster (Torrisholme) made a great walk!
For what it's worth, this is a summary of my figures:
Main Wainwrights: 214 fells cumulative: 516 miles 177,000 feet of ascent 50 days of walking.
Outlying fells: 116 fells cumulative: 205 miles 48,000 feet of ascent 27 days of walking.
(Most of the trips were day hikes to the Lakes: I live in the Yorks Dales so it's a lot easier for me than for others).
Post edited at 10:17