Now I know it would be costly for each end unit you apply it to, but the total number of end units that would require the modification would be relatively small. As such I'm starting to think that we could be surprised and see the number of units reduce to lengthen those that are remaining by conversion of the end units to central coaches.
For instance to lengthen the released fleet to 4 coaches would require 5 units (regardless as to if you have 2 units remaining as a 3 coach unit or if you end up with 2 spare end coaches), even lengthening the released fleet to 5 coaches would be 9 units (with one coach spare). Based on those numbers that would require the conversion of 10 end coaches to lengthen to 4 coaches (15*4 and 2*3 or 16*4) or 17 to lengthen to 5 coaches (13*5).
A 4 coach unit could have about 180 standard class seats and about 30 first class seats (with some variations depending on those numbers depending on how you set out the seats). Although that's not going to compare well against fully loaded 2*158's (4 coaches) it's still going to be more than a 3 coach 158 or 159 or a 4 coach 220.
Whilst a 5 coach would have about 70 extra standard class seats, putting it somewhere over a 221 in terms of seating, but again not as many as, say, a 444.
For instance to lengthen the released fleet to 4 coaches would require 5 units (regardless as to if you have 2 units remaining as a 3 coach unit or if you end up with 2 spare end coaches), even lengthening the released fleet to 5 coaches would be 9 units (with one coach spare). Based on those numbers that would require the conversion of 10 end coaches to lengthen to 4 coaches (15*4 and 2*3 or 16*4) or 17 to lengthen to 5 coaches (13*5).
A 4 coach unit could have about 180 standard class seats and about 30 first class seats (with some variations depending on those numbers depending on how you set out the seats). Although that's not going to compare well against fully loaded 2*158's (4 coaches) it's still going to be more than a 3 coach 158 or 159 or a 4 coach 220.
Whilst a 5 coach would have about 70 extra standard class seats, putting it somewhere over a 221 in terms of seating, but again not as many as, say, a 444.