I'd love to see another ex-NER loco, hopefully following the trend where manufactures doing pre-group have tended to do complimentary types from the same company. Several popular NER types have already been mentioned, I'd like to see either a J21, J27, or G5.
J21 very popular, long lived, could run anywhere on NER territory, and a preserved example currently being restored for modern interest. A word of caution on this one though, very similar to a J15 someone's already doing, so they're half-way there already. Not much more than a change of cab and tender, both being T.W.Worsdell machines.
G5 basically the standard NER passenger tank, ran anywhere NER pre-group till replacement by the DMU. New-build project nearing completion for modern image interest (or even possibly, tie-in).
J27 again a very popular engine, would run anywhere NER, right up till 1967, the last pre-group engine in service. Preserved example for modern interest again. Besides, my pair of Q6's would look lost without their little cousin!
Know you've a lot on already, so possibly by February?
....anyone would do!