It's certainly my view that there will be a "sparks effect" and significant suppressed demand due to the outrageous levels of overcrowding on the 185s, and that these sets will indeed be full very quickly. I reckon they will need to be extended to 7 or possibly even 8 coaches in pretty short order, that or put them on the Liverpool-Nottingham where they will be about right for demand and order more 80x.
Given that most of the overcrowding is on the core route of York to Manchester and that route will see double 185's on the Hulls, double capacity on the 802's and 100+ extra seats on the Mk 5's then I doubt these seats will fill up as many expect, bar peak services. TPE this time next year will have around 700 seats an hour extra. Maybe post TRU disruption we'll see these seats fill up quick.
What's clear though is that those 700 seats or so are needed ASAP... and we're not far off now!