Here’s my thoughts:
Steam:
A full-spec 9F Crosti
A WD 2-10-0
Possibly another influx of Railroad 9Fs, with preserved examples such as 92214 in its BR Green, 92134 as that has returned and possibly a rerun of Black Prince (that’ll probably be the case having just got hold of the 2000 limited edition!)
An S-160
Diesel/electric:
Any of the early AC electrics (classes 81-84)
43185 in its IC Swallow livery
The LNER Farewell HST
A rerelease of the EMT/EMR HST
Ex GC EMT HST
Blue Pullman HST
91119 in its IC Swallow livery
More class 87s, 87012 in its NSE livery or some DRS or GBRf 87s, or maybe 87101 in its late 90s BR Blue livery! I could see them doing a Bulgarian 87 as well to go with their European collection. (87004-8 perhaps?)
Coaches:
Mk4 coaches and DVTs
Retooled HST Mk3s and possibly the Oxford Mk3As but with minor changes to make them better suited, Mk3B coaches as well so then we can get a BFO, and more Mk3 DVTs in liveries such as Greater Anglia, LSL IC Swallow and unbranded BR Blue (82115)
The list goes on and on but they’re the main ones I can think of!