has to be either the one where gordons buffer beam was just called a buffer (which is ridiculous) or day of the diesels

"YOIKS!"

the only things i wish to see that would be the most likely are:

Diesel 20 (branchline have a class 42 warship)
Oliver(branchline has a 14xx tank)
Splatter
Dodge
Arry
Bert(all of them are 08 shunters  which can either be modified from diesel or taken from the branchline tooling)
Boco (branchline do a Co-Bo metrovick)
Daisy(branchline do the correct DMU)
The Old Express Coaches(just repaint Annie or clarabel and then the other 2 coaches will need a new tooling which goes the same for the red coaches)
the red coaches
old shape Henry(just put Gordon's boiler on Henry's running board)
Better Express Coaches (base them on the Si3d series one coaches at Least guys)
series 1 truck (just a standard truck with stickers instead of 3d faces)
MOAR Brakevans
a choice between different liveries on rolling stock in case we want Sodor mail written on the side of our Sodor mail coaches

unlikely/completely new moulds:

Lady
breakdown train
Diesel re-model as he looks too big and bulky  and should be smaller and should not have a smiling face but a series 2 smirk face

again these are what i reckon would make some decent profit margins if created over time and quite frankly its just suggestions and not a demand