Here's what my refurb would look like;
150: Chapman 2+2 like ATW's
155: IC 3000
156: IC 3000
158: IC 3000
170: IC 3000
319: Chapman 2+2 as per the 150's
769: IC 3000 & Luggage racks in front & rear coaches (can be removed after Windermere & Barrow services change to 195 operation) and same as 319's in center coaches
I guess you, like I, are a fan of the IC3000. Large-headrest version even better, I agree.
But I would go:
150: Thameslink style 2+2 Fainsa "ironing boards", no armrests, spaced 1" from the wall.
155: If you're not scrapping the terrible things, 2+2 Fainsa "ironing boards" with armrests per the ScotRail units. The pitch is so tight (and can't necessarily be changed due to underseat equipment boxes) so the thin seats will provide a real benefit.
156: as 155 for the same reasons. I really like the ScotRail refurb design, it should be copied exactly other than the seat fabric design. (I quite like the dark and light blue above, use that).
158: Grammer IC3000 in almost-original layout. To provide DDA compliance a few rows would need to be shifted around a bit, but the original layout as far as possible is by far the best use of space in a Class 158 (it loses[1] no between-seat-back space at all by alternating airline and table seats) and provides excellent window alignment.
[1] Yes I know, luggage space. Nobody *ever* seems to put it there. Better to use a layout like that and have dedicated racks as built, and maybe see if there is a way to make the overhead bigger/easier to access e.g. by redesigning the lighting conduit to be more flush with the ceiling using LEDs.
319: as 150. They are basically the same bodyshell.
769 for regional use: as 150.
769 for Windermere services (I'd send them to Barrow myself too, but I know the issues which aren't for this thread): Grammer IC3000 in a 2+2 layout with tables. Each full length two window section should contain 6 rows of seats, one side all airline with priority seats, one side 3 table bays. Or as an alternative, mix them up in a layout as below allowing the tables good window alignment:
[=[==][==]=]
[=-[=[=[=]-=]
where = and - are legroom, the ones with - are priority seats with extra space - if you do it with spaces it doesn't align properly! Though under seat equipment boxes may dictate which precise layout is possible, I don't *think* 319s have as many of these as 150s. Priority seats would omit the centre armrest for space due to the door pocket.